Well.. I'll throw out a couple of random ideas
I've never used that function myself... but I'm guessing that it could be for one of two things..
A) You could use it to create a random starting point along a patrol route? Like the AI was at their first waypoint five minutes ago? something ..
B)If you have extended map info.... I believe that you can see the vehicles and units on your map screen as you spot them.. and isn't there also a time next to the icon on the map? of how long ago it was at that spot ?
Just some speculation on my part, maybe someone knows for sure