Checking obstacles for players would be incorrect. There are a few cases when such check is excessive, like a creep stepping over a structure which will be destroyed at the next tick. These cases are more or less rare but still, it's breaking change.
As for your other questions, well, if you're asking this then you're probably experienced enough to migrate to PathFinder.search which provides lots of necessary information (sooner or later, this happens to all of us).