Well, think of it this way:
No matter what, it will be tile based. Either the ground will be split up into large tiles(like 5 units) or each unit will be a tile. If you do this, you will have to use every unit as a tile when doing ai. It would require large map arrays and that kind of stuff. Here are some examples of tile-based sims:
Sim City 1,2,3,4
Sims 1&2
Command and conquer
and almost all other sims. It doesn't really look tile based, because you can't see the grid, but it is still tile based.
I'm not trying to stop you from doing it this way, and it might not even be that hard, or it could be harder. I'm not an expert at this, but I know that it will be harder not being tile based than if it is. If you have an idea for how to do this, go ahead

I'm not trying to stop you.

Hippopotomonstrosesquippedaliophobia-Fear of long words