They're extended for landing and then retracted while taxiing to the gate. Some time passes, the plane is readied for takeoff, and the flaps are once again extended.

I understand why they're retracted in the air, but why on the ground? Retracting them on the ground doubles the number of cycles the mechanical parts have to endure, so I imagine there must be a good reason.

Speculation:
1) clearance under the plane for ground equipment, refueling
2) less chance of damage if flaps retracted
3) regulations
4) confirmation that the flaps mechanism is working (at least to extend) before takeoff

What am I missing?