If you are anything like myself, you like to play around with the settings on your phone in order to make it faster and just better in every way. You most likely have an Android based phone, because they are easier to customize. If you are really adventurous, you may have rooted your android phone (not recommended for those who do not watch what is happening to their phones, especially during installs of new apps, very carefully). I haven't rooted my phone, but only because I haven't gotten to it.
I like to read blogs on ways to make your phone use less data and ways in which you can speed it up. I was reading one of those blogs one day and following along on my Samsung Galaxy S5 from Verizon. Most of the settings that the article suggested changing didn't seem to do much, one or two did (for instance changing the screen to be more sensitive (it may even work with your gloves on) is as easy as going to Settings->Display and putting a checkmark in the "Increase touch sensitivity" checkbox.
I tried several other settings and then I came upon the last suggestion in the blog, change your OS to Android Runtime (ART) instead of Davlik. The poster did say this was experimental, but that it would make your phone faster. This sounded too good to be passed up, I should have done some more research first. I changed the setting and the first thing I was asked to do was restart my phone, this made sense since it was changing the OS. I restarted the phone and the startup screen said it was optimizing my 531 applications (yes that many, although I think there are more than a few Verizon, google and samsung apps that came built in). It took a couple of hours to count down and then it rebooted again. When it came back up it said it was optimizing around 150 applications. Not only didn't this sound good, but I was beginning to worry. My phone rebooted again and said it was optimizing ~120 applications. Now I was worried.
I called Verizon Wireless (in retrospect maybe I should have called Samsung - they had great support the previous time I called) and asked what to do. The support rep had me go through several steps to get my phone up and running again. Finally, she said I would have to do a factory reset. Luckily I use the Kies app from Samsung regularly to backup my phone. I had made a backup that morning. So I figured I didn't have much choice. I did the factory reset, mostly because my phone was useless unless I did something.
After the reset, many of my applications came back through the link to my google account. Some others came back through the Kies restore. Other applications I had to redownload one at a time and NONE of my preferences had been saved using Kies. So go ahead and use Kies, but use something else as well. If you root your phone there are plenty of excellent backup apps out there.
If you want to brick your phone, this is the setting to change. There are a number of articles out there that say to go ahead and try it - by all means, but caveat emptor!