Is it necessary to drain winter cover/

Being only about 1 hour away from Buffalo, I've seen a lot of news reports lately on that big snow storm (we got nothing), and my heart goes out to everyone affected by this freak storm.
Unfortunately, I believe that the weather will only get worse in the years to come, I would think it's our own doing, so my recommendation is for everyone to always be prepared and have a plan that you rehearse regularly with those included in it.
We've done a lot of work and preparation for those freaks of nature, and even though it's a lot of $ up front, you'll be glad you did it even if it's only needed once.
Poconos - I understand your theory behind keeping a cover clean and pumped off, unfortunately, in some climates (like ours), that's all it'll ever be - theory. In reality, I don't think most Canadians would ever be able to keep their cover clean, it would mean quitting your daytime job, or putting all those weekend chores aside so you can stay on top of your cover. and spending most of your other time from November to April fighting off the pneumonia you're bound to get spending countless hours tending to your pool cover. Most times, you don't even have an option since mother nature beats you to the punch and freezes the thing solid before you can walk out there with the pump. This is why i don't bother doing much of anything with my pool for/over the winter - covering it is a huge waste of my time and could lead to my pool getting destroyed in one winter (primarily wind), I'd rather spend 1 hour to vac up some leaves off the bottom come spring time, it would still only be about 1/50th the effort in comparison to a full pool winterization and maintenance thereof.