The Section 333 Exemption allows you to operate in the NAS without following ALL of the rules. The EXEMPTION specifies which rule(s) you don't follow but also stipulates how you are to operate when following the exemption. While this was widely used for Commercial/Civil UAS operations it is also used for other rules associated with full size aviation (like flying without doors or a seat so sky divers can jump out of the plane etc).
Under our Exemption we had to make contact with, and get PERMISSION from, the controlling authority (tower or airport authority), have a Visual Observer, and do a lot of monthly reporting.
Flying under Part 107 is a LOT easier from a business point of view. Unfortunately my 333 Exemption expires in 3 months and I won't be filing for a new one.
Contrary to what many are saying, the Section 333 Exemption process isn't going (or hasn't' gone) away but with Part 107 we don't need it for "Commercial/Civil" UAS operations. It was merely a way to operate within the NAS legally until they created a better solution.