The kitchen is pretty much always blocked off these days since Sam can't be trusted in the kitchen, but before Sam was mobile, we still used it when we wanted to keep Wil out of the kitchen, such as when we were cooking.
The top of the stairs gets blocked at night time so Wil doesn't accidentally fall if he runs out of his room (he's had nightmares on occasion) and if Sam is roaming free upstairs.
The bottom of the stairs gets blocked when Sam is roaming free or, and this is the fun one, when Sam is upstairs sleeping and Wil is not. Wil likes to go upstairs and wake Sam up to play. Not kosher.
So, enough about gates, but that's my life.