There are many reasons that come to mind, besides BSA is going to require it soon. The chief one is that we want the best scouting experience for the scouts we are guiding. Luckly, the group of leaders I work with is great because we work together and share knowledge and experiences to make life for everyone easier and to deliver the best possible program to the Scouts we work with.
Sharing the responsibility of advising the new den leaders to talking to the prior year leaders to see what worked well and what didn't. It makes the incoming leaders job much easier and the sharing of ideas a better program for the boys.
Please feel free to share what has worked for you, your Pack/Troop/Crew.
Thanks, PackTrainerSteve