If people didn't do covers at sessions here would be no cross-fertilisation, no exchange of ideas. But the difference is between the guy/guyess who comes along and does the same party piece they always do in the expectation of praise and acclaim, and someone who thinks - "see what they make of this; I wonder if anyone knows it?". There's also the common situation where yopu need to do a familiar song in order to keep everybody engaged. OP obviously a session noob.