I always use them, except when launching from ramp with dock. On flat ground, or gentle beach, it is easy to move the boat single-handed. On steeper inclines or softer sand you may need a helper.
As the others have said, eliminating wear & tear on hulls is key.
They've been well worth the $$ I spent on them. I've done zero maintenance on the wheels in 8 years. They're in the sun constantly, the rubber is fine.