The base tracker zooms out to fit the entire base automatically (including outposts). It does this by keeping track of what you build, so for an existing save it will ignore the existing buildings. There is a button to recalculate the bounding box of the base. But this is something that you do not want, as it will include your outposts as well. So instead you could 'initialize' the base tracker by building (and removing) buildings on the corners of the area that you would like to keep track of.
Pro tip: When you build another outpost that the base tracker should ignore, you can pause the tracker. It will ignore the miners, stations, etc. you build. When you unpause the tracker, it will continue tracking the things you build next.
The area tracker keeps track of the defined area, it will not automatically resize. It can be used when you plan to build something, and want to show the complete build area without zooming out gradually. For example, you could focus the tracker on the ore field and the (planned) station and build the whole thing.
It is up to your ideas, inspiration and editing skills to select what tracker(s) you like to use. Basically when you don't have a plan for the final timelapse the area tracker will just keep tracking everything. If you have some sort of a plan, e.g. zooming in/out of certain areas where you are building you could use the area tracker (and smooth zooming enabled on the camera).
Good luck making a cool timelapse!