I only write poetry in verse form when I can't come up with any ideas. I much prefer writing in free verse, but if I have committed to writing a poem (i.e. for NaPoWriMo or another challenge) and just can't get inspired, I force myself to write in form of some kind. The exception to this is the villanelle; I LOVE villanelles and write in the form frequently because they're fun. But I dislike writing most other types of formal poetry (reading is a different matter; I love a well-crafted piece of formal verse), so I challenge myself to write in form. I'm not sure what I hope to accomplish by doing this. It's not like writing in verse gives me inspiration for free verse poetry. It's not like making myself write verse is the type of negative reinforcement which stimulates me into not getting writer's block.
Also, sestinas always confuse me. I screw up the form several times before I can actually get something that follows the form properly.