Always ....... be sure that you or the person you are talking to is describing actual "hull speed" which is always your speed thru the water.
When you read off the SOG from your GPS, that's different thing altogether. Very useful for estimating your ETA at a destination, tho!
(I notice that a number of younger boaters locally do not know the difference. And since we boat on a river with variable current, and even that slows a lot or even reversed twice a day with tides, one cannot base their opinion of their boat's performance on SOG. At all.
For example, last weekend, we had almost no wind and motored up river to a club cruise at a state park. We carried the last of the flood tide with us part of way and our speed and SOG matched, and then we hit the true current and our SOG slowed a lot - down to 5.8 from the previous 7.1. Returning home, downstream, we were hitting 9.1 over ground (SOG) in some narrow stretches. Fun Stuff !!