Personally speaking, every few months, and especially after an update, I will move the current .ipsw file to my trash bin, put my device in DFU mode, connect it to iTunes and then when iTunes detect that it's in recovery, I will select to restore and update. This forces iTunes to download and then install a fresh copy of the latest iOS version. I like doing this because it keeps my device running problem-free for the most part. It's not necessary, but it is something I simply prefer to do. Do any of you do this or at least erase all contents and settings periodically?