Myself, i fall on the far end of Theater of the Mind. I use maps that are revealed on screen using Fog of War (Roll20 is our VTT of choice these days) but we don't use tokens, we don't stress exact placement and my players put a lot of faith in me to run things fair and square (I do believe that successful Theatre of the Mind style play requires player trust). If one of my players were to put himself and their party in the way of a "fireball blowback" I'd be sure to give them a hint of such a possibility as they announced their intentions.
I'd expect that "use of a grid" leads to a more precise spell interpretations than the "Theatre of the Mind" style of gaming, but I could be wrong.
I'm not saying one style is more correct than the other, as the rules support both extremes out of the box, at least until late in 3x.
So, thoughts, comments, questions?