You empty the basepaths because EVERYONE SCORES. Why in the world would you prefer to be down 2 runs with a runner on over being down 1 run with no one on, when there isn't any difference in outs? It's the perception of the homerun serving as the rally-killer. Either way, the guy at the plate has to score, so that doesn't change. The difference is, the runner at second keeps the pitcher in the stretch/under pressure/whatever. I don't know which way I'd fall on this one, but I at least understand the thought process. Well if we're going to use that logic, take it all the way. It's the 9th inning, so up 5 runs the other team probably didn't bring out their closer. Before the grand slam they probably did, as I doubt they let an inferior pitcher/tired starter allow the other team back into the game. So now the closer is in and he just gave up either a bases clearing double or a grand slam. It's obvious he's not lights out today. He's a closer/reliever, which means the odds of him throwing from the windup are slim regardless of the situation. Does he care about the runner at 2nd(if he hits the double)? Nope, that guy's run doesn't matter, so he's not getting flustered thinking about a potential steal(which tangentially makes the number of outs in the inning irrelevant). So in the end from the pitcher's perspective, there's no difference after the fact. He needs to keep the hitter from scoring and that's what he's worried about. Which means as the hitting team, we take the run in hand 150 times out of 10.