Advantages: -more area covered = more plants in the same space = more bud
-less heat because warm air rises and it doesn't get trapped in a reflector
Disadvantages: -depending on how your tent works and how big it is it can be a pain to water and train your plants (but I imagine without topping you won't need to train much just to tie your main stem to a stake or something)
-you will need special glasses to work in there otherwise you're gonna be facing massive headaches, especially with a metal halide
I've done this before but with my little space the disadvantages outweigh the advantages but I am surely planning on doing something like that with a bunch of untopped indicas