Currently, it seems that love.timer.getTime is simply a less accurate version of love.timer.getMicroTime.
The wiki says that love.timer.getTime starts at an unspecified starting time. Checking the source, love.timer.getTime seems to wrap SDL_GetTicks converted to seconds, and it makes sense that this number wouldn't quite be equal to the time that the game has been running. So I can't see why anyone would want to use love.timer.getTime instead of love.timer.getMicroTime.
I propose that love.timer.getTime be removed, and maybe that love.timer.getMicroTime claims the name love.timer.getTime, although that name kind of implies it returns the current local time.