You're probably seeing a bit of news that the delta updates for Play store applications that Google talked about at I/O 2012 have went live today. Coders, web developers, and Android geeks love this sort of thing, but I'll imagine quite a few of you are asking yourself what these new delta updates mean for me, and do I need to do anything or worry about it? Let's try to answer that.
A delta update is a broad term that means only changes to a package will be downloaded and the changes will be merged into the existing files inside the package. In this case, the package is the apk file that's installed on your phone. To try and keep things simple as possible, let's use an imaginary app called Cool Widget. If you already have Cool Widget installed on your phone or tablet, and the developer makes a change that gives it a new background, you won't have to download the whole thing. Google will do a version check, then send out a patch that merges changes the developer made with the files you already have. Besides the obvious -- the new background image itself -- there may be changes to some of the code, or in the manifest file, so you'll get a delta update that copies the new image to the apk file, erases the old, and merges those code changes in. It's new for applications in Google Play, but it's how Google has been sending out OTA updates for Nexus devices (and a few others) for a while now. In the end, it means less data is used and sent.
For users (that's you and me!) it's not a big deal. Sure, we'll save a little bit of bandwidth by only downloading parts of a big file, but the really big downloads (think game assets) are usually hosted elsewhere and installed after the app is loaded the first time. Every byte saved counts though, especially if you don't have unlimited data. Just don't go thinking this will make a difference in your monthly allotment -- keep using Wifi to download big stuff if you need to monitor your usage. The real benefit is to Google, who serves millions of files through Google Play every day. Small amount add up quickly when you're talking millions, and less data being sent means less bandwidth and server time used.
As for what we need to do, that one's easy -- nothing. This was a server side change. Keep on installing and using apps from Google Play as you always have, and update them just like you're used to doing. The best changes are transparent to the users, and this is one of those cases. Nothing about the way you install or update your apps has changed. Google does a lot of things that confuse (and infuriate) us, but this time they did it right. In fact, if it weren't for all the eyes of some smart people on the Internet, we wouldn't even know it was changed.