Well, if each unit leaves its own scent trail, that’s a lot of per-unit state, and little to nothing that you can pre-compute for the entire map. You could have all units trails on a global “scent layer” that all units read from, but then you’re basically just building up a graph of common paths that could have been precomputed for the entire map.

It also doesn’t at all address inter-unit collisions, which is a big topic in RTS pathfinding.