There's a server/client RTS engine called ORTS. In one of their documents, "On the Development of a Free RTS Engine", they mention basic gameplay tasks, like pathfinding, are implemented client-side ("Low Level AI Components" section of the document linked below).
This sounds like a good idea because it offloads pathfinding (a potentially expensive task) to the client, leaving the server free to take care of other tasks. However, wouldn't this give an unfair advantage to clients with a faster CPU?
One option is to force pathfinding to take a max number of frames on all clients. But wouldn't this take away part of the advantage of using a server/client architecture (not waiting on the slowest client)?