A lot of the necessity comes from tank size, type of corals kept, amount of units and how large the corals are.
If you can post some of this, it will help. For example, a 2 foot cube with a pair that is a year old has no need for supplemental lights, whereas a 72x36x30 with acropora colonies might need supplements with 4-6 units, but not with 8-12.
There is a lot of nuance in this.