Distributed grids with lots of generation points have their advantages but are really hard to manage. Somehow I doubt this is going to go to the point of having a small fusion reactor in every building, so we have to have some kind of grid. Large-scale generation is something we could plug into the grid we already have, which is a distinct infrastructural advantage - if it turns up before we have solar panels on every roof, anyway.

They're also not suitable for small-scale energy production. You have to put in more energy (to accelerate the ions towards the center) than you can get out (as heat).

Well, you also need to generate more power then the fusion device consumes.