I can only go by what I see, (Belichick's line) In the last 10 yrs our smallish school has had 3 baseball players go D1. All 3 were what most would consider players with average physical gifts and only played baseball. We've had a good number of players who seemed to be more athletically gifted that played football AND baseball. None of those players went on to play D1 in football or baseball. It all depends on what your kid wants from his experience. Lebron played football, baseball and aau basketball through his sophomore year, it wouldn't have mattered if he'd played tiddlywinks, chess, and basketball. He was that gifted. If you're a physically gifted athlete and can play several sports, that's great if that's what YOU want to do. I think some are pushed into it by parents and coaches and it really isn't their choice.
If the player is a borderline athlete and has his heart set on playing at a D1 school, my advice would be to take care of your body, reduce chances of injury (ACL, concussions, breaks, shoulder separations, all injuries I've seen first hand sidetrack local kids) by playing the sport you love and building up the muscles you need to play your sport in the off season.
A player from our baseball team who is getting some D1 looks was getting some pressure from some people to play football next season. (We have 5 that do) For about 2 weeks he was considering it. His dad was ok with it, his older brother didn't like the idea at all. He now say's he's not playing football.
I just think that if it's such a great idea in high school, why don't college and pro coaches encourage it at those levels? Athletes at that level can over train as well, and there are some that are gifted enough to pull it off.
Each individual gets to weigh his options and make his own choice, there are no set rules, pros and cons either way.