The only time a group impacted my cruise was when a wedding party seemed to have reserved the same spot every night. I can't even remember the ship we were on, but I really, really, really wanted to go to the piano bar. We tried on three separate nights, and each night, a large wedding group had the piano bar reserved. With my luck, the piano bar was probably empty on the 4 nights I DIDN'T try to go there. Oh well, not a huge deal, and certainly didn't ruin the cruise.