Yesterday I reached the end of my first 3 month power down, and upon trying to transfer my STEEM to another wallet, found that I couldn't because my "bandwidth" had been exceeded - in short (as gleaned from a few disparate posts) because I didn't have any Steem Power left, and that was what influenced my allowed number of transactions.
Not only this, but I couldn't cancel any ongoing power down, upvote (I didn't try this personally but another post querying the same problem stated this, and it makes sense), pretty much anything.
The only solution for me in the short term was to buy more Steem Power in order to be able to access my funds, which was a bit of a bummer. Whilst I understand Steem Power is a way of encouraging people to keep some investment in the currency, and think that's a great idea, as a semi-casual user of the currency it left me with a bad taste in my mouth. If I'd have a) been aware of this mechanism or b) been able to set a minimum retention, I wouldn't have felt the same feeling I'm sure they get when they send a "small payment" to a "Nigerian prince" in order to "access their funds".
Of course, it all went just fine in the end, but I thought the community might benefit from my experience! I didn't have 0 Steem Power, but near enough, and depositing about 8 was enough to allow me to carry on using Steemit again :)