Injury prevention: Strength training provides improvements to bone density, joint integrity, muscular support, muscle balancing. This is a huge benefit to an athlete performing repetitious activities. I was a very injury prone runner, continually out with injury. During this season I suffered only moderate impact injury to my left foot that healed in two weeks and an ankle tendinitis. To me this is a huge benefit and reason enough to strength train in the off-season. An athlete that remains injury free is an athlete that can train at a higher volume more consistently then another. Looking good: An athlete happy with their body is more confident and you could argue a better athlete because of it. Plus the wife likes it. Maintenance: Maintaining physical activity during the off-season and allowing the sport specific muscles and injuries to recover. Variety: Weight training is fun and variety prevents burn-out.
So what do I recommend? I recommend an off season strength training regimen to provide adequate time to heal from a year of sport specific training and for the benefits of injury prevention. After that take it or leave it. If you feel it provides continuing benefit I would utilize the program I outlined earlier until it begins to inhibit your progress and take up valuable recovery time.