Well, in one world I used my first diamonds on enchanting table, refinery, assembly table, laser and finally energy cell.
Edit @KirinDave Overall energy is not something that is hard to generate. On my world I don't play FTB insanity, I don't have to be 100 % efficient with given set of mods, I like to explore mods and try out different combinations. Steve's cart farm is fun to build once, nether lava also (well, without using item teleportation techniques moving lava pump adds a little bit of fun with building nether tracks, but it is still extremely powerful).
Also, about sucking energy. New farms use energy only if they have something to do, I run my silly wheat farm (most expensive 5x5 multiblock) with 2 MJ/t input on REC next to the farm and cell is staying full (output 100 MJ/t).