If you leave them soaking in bleach, then the bleach will eat away at the cotton in them. Depending on the strength of course.
They will start to look a bit grey after a while, but will still do the job just as well.
Had mine 18 months now.
I heard about all the weird and wonderful ways to clean them as in the soak in M power etc...
I have found that a good hot wash with a soap powder (no fabric softener though) does the job perfectly well.
I do not use the ringer bucket method, so cannot soak them in that as I aint got one..