Downsides? They take up a fair amount of space, so you must pick and choose. Also, there's no need for an Internet connection to access them. Once redeemed, you "own" the downloaded files and can easily transfer them to digital devices on demand (well, as long as they're iOS-based). The nice thing about iTunes Digital Copy downloads is that there is, in fact, a feeling of permanence. Disney codes routinely work after the expiration date, while I've found that Warner Bros movies consistently fail. Some studios are more forgiving than others. When I realized my mistake, I redeemed all of the codes I could find that still worked. The codes were generally only good for a year, but I thought this meant that the digital downloads themselves were time-bombed and would stop working after the date had passed. Years ago, when digital download codes were first being bundled with DVDs, I resisted redeeming them due to what I imagine was a common misconception. It required a lengthy adjustment for me to appreciate the value of keeping movies in the cloud. Then, after dinner and some light TV, most nights I'm ready to play.
Then, in the evening, I'll frequently pipe a favorite flick to a small TV in our kitchen while I cook or clean dishes. So I prefer using my iPad, much in the same way people will listen to music in the workplace. You could sacrifice a second screen and some of your computer's processing power to stream a movie, but I find this slows me down too much and blocks me from my second screen, which I use constantly. You could watch a DVD or Blu-ray, but those take so long to load.
The challenge there is portability and the ability to get in and out of your movie collection quickly. If you're like me, you also find it soothing to listen and half-watch a favorite flick while performing a repetitive work task. Watching a movie, particularly one that you know well and quote often, can relax you and help get you ready to get your game on.
Games take a certain mindset that you may have a difficult time easing into after a busy, stressful day. Part of the challenge of being a busy gamer is finding the energy to interact with a game rather than simply kicking back with less engaging fare such as movies and TV.