But since the purpose of the Visa Exemption is temporary visits to Thailand and you use it to stay long time in Thailand with borderbounces you might end up in trouble if the immigration officer do not like your "missuse" of the Visa Exemption scheme.
Depends on how often you do it. Its all up to the immigration officer to decide since there is nothing in the law about how many times you can do it before getting in trouble.
As long as you dont just turn around at the border every time and go back in again there should not be a problem. If you show that you are also traveling in other countries in the area you are OK because that is the way Visa Exemt is supposed to be used. Its when you start using in for a longer time to stay in Thailand you can get in trouble.