When I work my horses, I only school them about 1-2x a week, with each session lasting roughly 10-30 minutes. The rest of the time I ride around the farm on a loose contact.
The reason I believe riding on a contact is important is to teach horses how to be supple in their body, and how to find softness in their jaw so they are light and loose when you turn, stop or do downward transitions. Once my horse has dropped down onto the 'contact' I try to push my hands forward towards the horses mouth as if I were pushing wheelbarrow handles. This allows my horse to work into the bridle, as opposed to working backwards with their head pulled into their chest which can be very uncomfortable for the horse and in time can lead to muscular and skeletal issues.