As someone who is on one of the lowest pop servers in the game it's far from a barren wasteland and their are many benefits to it. For one I won't be sitting in a queue on Friday morning, I'll be playing heavensward. Like when the Gold Saucer was dropped people on Gilga had to wait to queue into the area due to it reaching max capacity. On my server no such thing happened and it was still packed.
And another is that while there are less people there is much more opportunity in everything including things like server firsts, crafting, markets, housing and so on. There is also a tighter sense of community on smaller servers.

More people =/= better for everyone. Better is an opinion. I personally prefer a less populated server but I can see why some would prefer a larger one. It's all preference.