I've only offered advice/observation a couple of times. Onceto a lady who was exceedingly slow with a grueling cadence up a grade and complaining to her companion her knees hurt. I stopped and after a brief chat I raised her seat. Incidentally, small front, big rear for hills was also news.
To one or 2 people, I've mentioned that their road bike tires looked about 35 psi. They didn't know 85 min up to 110+ would be better. (it also explained their rash of flats) I only mention because sometimes low pressure isn't obvious until you are 3 miles out of town and now it's flat. Having a pump and patch kit on hand is useful if you are going to open your mouth.

So, my summation is this: Barking out unsolicited advice is in bad taste; Unless you actually see someone having difficulty that you can actually assist with, then you should be prepared to assist.