PHP uses files for storing sessions; you do want to restrict where on your site you are using sessions as they do have side-effects. Most notably any page serve

PHP uses files for storing sessions; you do want to restrict where on your site you are using sessions as they do have side-effects. Most notably any page served in a path configured for sessions will have an expiry time in the past and a bunch of no-cache headers; for a dynamic page that is the behaviour you want, make sure it's not being applied where it should not be.