The first reason to take an off-season is health and durability. It’s always been interesting to me that the American baseball population, which many times only started baseball in the first place because they perceived it to be “safer” than other sports, stubbornly ignores the research that clearly demonstrates what a catalyst for injury playing year round is (PMID: 16452269 PMID: 29630388 PMID: 26797699). The simplest way to reduce injury rates: take a break from the repetitive, cumulative trauma that playing year round is.
Another benefit to taking an off-season is development of overall athleticism. If you have traits: ie genetic talent that allows you to be more successful than your peers “just because”, then yes, you’ll be fine without playing multiple sports. But for the average talent baseball player, playing other sports and exposing themselves to multiple movement patterns is a critical piece in building the athleticism they need at the higher levels
Lastly, there’s a very real positive mental benefit to taking an off-season. Sadly, year round, year after year baseball leads many athletes to burnout. The human brain thrives on novelty and adventure, and 10-15 years of year round practices, games and tournaments becomes monotonous. The consequence is many athletes begin to pull back, often in the years they need to push the hardest and persevere from college to Milb, to ultimately MLB.