I had flaky power steering on an old Lexus LS400, and it would stop working for minutes at a time, more or less at random. At 40mph, I could generally tell that it wasn’t working but there was no meaningful extra difficulty when steering. At 15-20mph it was quite a bit harder to steer. At 5mph, it took some real force to steer. At parking speeds, it was very hard to make the large wheel movements needed to park. At a full stop it was almost impossible.

In general, this wasn’t especially hazardous, since I rarely needed to move the wheel very far while moving at very low speed in a place where other cars could be a hazard.

(Yes, I got this fixed. And the old LS400 cars were extremely well designed and built.)