Can someone either link me to or supply me with a tutorial on how buffer depots work? For the life of me I am unable to figure out: (this is after spending around 2 hours looking around both google and youtube for a guide on what they do). From what I can gather they have something to do with excess production and some sort of priority but shrug
1.) what their purpose is?
2.) how to use them effectively?

They are basically used, to the best of my understanding (others may well give much better insights) to be able to request materials to be near your requesters, but I haven't really found them to be useful. If you could put items into them directly, I could maybe use them as storage that would be used up first, but as it is, I don't use them.

Basically you place a buffer depot someplace on your road close to where you will need whatever it is you are transporting. You throw a bunch of drones into the buffer and those drone make the long trip back and forth from the supply. Then, you place your requester depots where you need them for you factory with only a few drones in them. The drones from the requester would grab what they need from the buffer. It basically allows you to have a supply hub of sorts. If I have a buffer that has to make a long trip to the supply I will through a ton of drones in there. 100 isn't unheard of. Then, my requesters close by might only have 2-5 drones.

Also, it does act as a buffer. If the trip is long it is possible for the machines that the requester is feeding run dry before the drones get back from the supply. The buffer depot removes some of those issues because there is a large supply close by. If you add a depot writer to the buffer depot and set it to the requested item = xxx you can set the buffer to even greater levels. When my factory really gets moving and the amount of materials I need increase. I will add a buffer depot and have the depot writer request 100k. Just remember. Drones always pull from the closest depot that has the supply of what they need. So sometimes you may accidently setup a buffer depot with a ton of items in it that get ignored by the requesters because there is another smaller supply closer.

In short, it acts an awful lot like the buffer chests in the logistic network...only with drones.

Now, my question is do buffer depots rob from each other...I'll have to set up and experiment. (no they do not)

Have anyone been able to make buffer depots actually work instead of just theoretically with a video showing it or maybe some images of it working? As far as the theory states, they behave like requester depots SO THEY SHOULD REQUEST STUFF and also works as provider depots. But its not the case. I put in a test world a requester depot right beside a buffer depot and a mine over 100 tiles away from the buffer depot, no trucks get departed to fetch the ore, and the trucks from the requester depot are moving to gather the ore as they need but the trucks inside the buffer one are just sleeping and do nothing.

Only way I think they work is if I separate the networks but if I have to separate the networks there are plenty of solutions on how I could improve this behaviour. Since they should operate like buffer chests, they're failing miserably at it.

Never had an issue. However, I'm pretty sure that they take a lower priority then requesters. So...If your requester is full up you buffer will then fill up. Couple it with the included depot writer and you can set it up to be a large local buffer.

That's not how the logistic buffer chest works. The buffer Depot should work like the Logistic Buffer Chest, where you make the buffer chest between your supply and your requester chest to shorten up the travel time of bots. If you have a buffer chest and a requester chest in your network, they both work at the same time provided you have the supply for them. Its not an either-or situation. They both work at the same time. You put a request on requester chest, a bot will pick things up to deliver to it, you put a request on the buffer chest, a bot will pick things up to deliver to it, they're independant entities. Now if only when my requesters are full is when the buffer will start working, means they're only good to increase storage numbers, not to shorten travel time as the information description says. In other words they're useless, since I can just use provider depots to do that buffering and I have more flexibility with the buffer as well.

So if buffer depots only work when nothing else is working, then they don't work!

They stop working if there aren't enough items in the system, in which case its your problem to fix

I had 6 mining depots filled with iron ore, they were around 300 tiles away from my consumer requester depot. I placed 1 truck on the consumer. Then I placed a buffer depot on the same road as the requester depot, just above it but closer to the mining depot than the consumer. Placed 20 trucks inside the buffer depot, assigned it to iron ore. The requester depot kept sending trucks to the mine because the buffer had 0 items to be grabbed, to test if the requester would actually grab from the buffer depot, I manually placed a ton of iron ore there, they emptied out the buffer depot, no trucks got delivered, the requester then began sending trucks to the mine.

Yes I was consuming more iron ore than the truck was able to transport so it was always out doing deliveries even with the buffer depot having items the truck never stopped, I had this behaviour to make sure the consumer would want items to test if the buffer depot would work. It didn't.

So, my later test was use the combinator thingies to force 150k iron ore request on the buffer depots, I waited around 10 minutes before destroying that entity and it was empty still no trucks being sent to pickup iron ore and yes I had fuel in it, I had 20 trucks, I forced 150k request on the buffer, I had 1 mine working to fill their internal buffer and 5 mines idle with their storage filled up waiting someone to pick things up. Curiously enough when I took the trucks from the buffer depot and put then directly into the requester depot, all 20 now were en-route to the mine to pick up iron ore.

My conclusion? Buffer Depots don't work, at least not as intended.