Get a rope or even some fishing line wrapped around the prop and it can be more than just a little aggravating; it can land you in big trouble and calling for a tow.
The majority of ropes and lines are made from synthetic fibers, and while these may be great at tying things up, like your boat to the dock, they can be a real headache if they get wrapped around the prop.
A moment's lack of concentration and fishing line can get wrapped around an outboard's propeller, where it will swiftly work between the gear housing, damaging critical oil seals and melting into a solid lump that will require considerable time and effort with a sharp knife to remove.
It's bad enough on an outboard, but wrapping a rope around the shaft of an inboard-powered boat may require an expensive haulout to get things sorted. Be aware of lines on your boat that may be trailing in the water, just waiting for a spinning prop.
And watch the water ahead for floating line as well as other problems.