in my case, personally?
I use it because the ideal Nauvis is a sandy planet with very few trees.
To the point where it's a struggle to build power poles.
It's a simple aesthetic preference of mine.
(and I don't like dealing with deforestation, it's a hassle)
There are also some mods that require the use of a lot of wood, but the ways to generate wood can be very annoying or slow.
(O_o) And that's IF the mod includes any way to gain an automated supply, a lot of them don't; kicking the can down the road. The road leads to many places, here's one of them.
Honestly if you're thinking "why would i need this", the answer is that you probably don't.
