Keeping your own SP makes sense. You will keep your influence on the network and your upvoting power just like now. You are also not depended on pools.

Extra demand for SP can come from apps that need SP to onboard more users.

Also, realize that in the future it's unlikely that a user will realize they are using Steem when they use an app. 

Example: if someone is introduced to APPICS they will earn APX tokens on that app, they will never see that in the background Steem is used.