You only need to do it once. Period.
I'm not sure what the big deal is about wiping more than once is, it literally takes about a minute to wipe data/cache and then cache twice each.
RubiX Beta by Drod2169
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It is not a big deal to open and close all 4 doors of my car before I start it each time but if it serves no purpose why would I do it?
depends what you've eaten. taco night could bring multiple necessary wipes..
but seriously wiping data/cache more than once does help. ive had system files left from roms when ive wiped only once. not many, but it happens. and my ocd is always present as i wipe data and cache partition 3 times every rom change
With this being flash memory it's written to once is definitely enough. Once you tell it to erase, it's gone. It's not like wiping your butt where there's leftovers, or sweeping your floor or wiping crumbs from your table. This is something entirely different. If anything you're wasting read/write cycles by doing it which is shortening the life of your phone.
A hard drive with a platter, or probably even your sdcard in the phone would be a different story. Even though you tell it to erase the data, technically it's still there. Even in those situations you would still only wipe once unless you were worried about the data being recovered. That's a situation where you would wipe multiple times or make multiples "passes" where 1's and 0's are written many times over to make the data as corrupt and unrecoverable as possible.
i watched too much mr wizard as a kid
i could be wrong on the flash memory part and the read/write cycles but the rest is pretty much spot on. i know that you can wear out solid state disks but i dont know for sure if those same problems would affect the flash memory in this phone.
either way - yea, erasing it once is enough.