I use low level spells for low level dedication. If you just want 1st or 2nd lvl spells, you don't have to abide by as many restrictions of the faith.
I think of it more as a Vow of service taken for the major Power.
A minor dedication grants minor abilities. If you act grossly out of accordance with the faith, the spell list can be denied. But it's more lenient.
With Clerics/Priests/Rangers, it is a Vow but also a full Devotion to the Power. Full Devotion would allow much higher lvl spells, but also have many more restrictions and terms of service.
And then there are Pacts, Covenants, etc..