it's good to run the same route cos you get a feel for it, also you should know what time you should be doing on it
it's good to run different routes cos it stops you from getting too bored. I also tend to include hills sometimes and if I'm almost home but still feeling good then I'll go off in a different direction
so I've got a short course with 2 fairly evil hills, a long flat course that I know my times on, and some woods/parks round here to run in if I want to see pretty stuff - ducks, flowers, trees, girls etc
disclaimer - not a pro but run a fair amount