never heard you have to leave for any specific amount of time, although it up to the IO if they believe you are a genuine tourist. The good thing about Renong is they tell you before you leave if they will let you back in, so don't do it on the very last day of your permitted stay.
It's handy to make payments and not withdraw 20k baht at a time as paying 220 baht on every small withdrawals is silly. Good if your homeland bank rips you off on ATM exchange rates as you can send a large sum in one go via a money exchange service when rates are good and keep in the Thai bank. Useful to pay bills and pay for phone packages too. Was handy to buy a car too.