I don't know if this is an off-topic post, but I am very glad that you can get APK files of apps, or make them from the ones on your phone using something like File Expert.
For one, especially if you have "wiped" your phone and are starting over, it's much quicker to simply install already-downloaded APK files you have on your microSD card than it is to go to Google Play, and use the stock keyboard you maybe don't want to use, create an account, accept the terms, maybe wait for the Play store to update and on and on--and wait for the apps to download. With APK files, I can set everything up RIGHT NOW without any of that, and it's also not dependent on the quality of the data connection. You can always update apps to the latest version later, but when I've wiped the phone and am now "bare," I want a very quick "turn around" time to be up and running, I wish for that to happen NOW, with no delays at all.
Also, sometimes they change the apps in ways you don't like. For one, I hate the latest eBay app (created sometime in late September apparently), the one I have from circa July or August, I much prefer it. The latest one is just awful. If it weren't for APK files, I'd have no way of getting the older, better version. Also, the keyboard I prefer, Touchpal, for some reason took out certain buttons (DEL, HOME, END) in its edit/clipboard panel, and there are just "dummy" keys there. I can't imagine why in the world they would do a thing like that.
So, for such reasons, I like having the APK of the older versions, and frankly, I don't see where it would be wrong for me to share these with others who, say, have phones which auto-updated because they forgot to turn off that setting (I always do myself) and now they can't "go back" as it were.