Is clearing session data for edge caching mandatory?

I try to replicate the Forem caching system for my Rails app. I just wonder if there is any security issues with keeping Session cookies while caching a page?

In Forem's controller concern, which sets cache headers, request.session_options[:skip] = true is skipping session cookies.

Could someone explain to me why? I use session data in order to redirect the user after login to the last page visited.

Thanks for your help, I am quite a noob about caching!