rellhom If this option is not enabled, and you switch away from a profile, the apps in the profile will be stopped.
If you want the apps in the profile to keep running when you switch away, don't enable that option.
Often people install a messaging app in a secondary profile and hope the messaging app will receive messages or calls when a different profile is selected to use the screen. If the apps in the switched-away-from profile have been stopped, they can't receive anything or provide notifications.
rellhom Is it best to have this off?
That depends on the user's intentions for that profile.