Cross-training can keep a person motivated to exercise, assist with working around injuries, encourage performance based work rather than a constant dreary focus on fat loss, help people find skill or interests they may not have realized they had, provide opportunities to be fit in multiple areas (strength, balance, flexibility, cardiovascular fitness). It might be a way to engage with other people who like to exercise. Prevents boredom and burnout (overtraining). It also may allow the body to recover, such as providing exercise options on non-weight lifting days that do not interfere with muscle recovery.
All great answers!
Yes, you will help reduce boredom and overuse injuries, but one of the best reasons to cross train is that it gives you an opportunity to discover a new way to exercise or a new sport. Not to mention the change in exercise shocks your body and increases your potential for fat loss!