Quite simply what it says it does. This mod replaces all vanilla pipe textures with higher resolution ones.
Apart from being higher resolution (4 times as defined) the visuals of all pipes has changed. While i could spend hour on end trying to replicate all the visuals of pipes in Factorio, i decided to do my own take on what i feel they should look like.
These pipes also come with their shadows separated. Which means no more strange edge cases where there's shadows that should or shouldn't be there.
Also, the shadows are softer (using nicer render settings) AND they cast off to the right rather than down-right like vanilla. Thus making them less intrusive in tiles south of the pipes.
AAAAND, the pipes are tile aligned. As in, you don't get strange offsets. Their centers exist at exactly .35 units above ground. Their ends connect at .5 on each end horizontally and sqrt(2) / 2 on each end vertically. Square root of two because that's how the games tile engine works.
Because of this alignment, you are less likely to need to use sprite shifts in graphics that connect to these pipes.

Also, vanilla pipes had strange positioning. Mainly, they were offset on the x-axis ever so slightly which annoyed the living HOOHA out of me and my sense of perfection.
Not only that, vanilla pipes (as far as i could tell from matching them initially in 3D) are sunk into the ground.

The downsides to using this pack is that pipes will definitely mis-match with A LOT of other contents that connect to pipes. Both in color and in alignment.
So use it if you want to have nicer looking pipes that are better aligned at their core for future projects.
No-one is forcing your hand though.

NOW INCLUDES BOB'S LOGISTICS PIPES