@Mma ******
He could get pulled aside and questioned for doing this. Unofficially at least, Thai immigration really only likes to see one extension on a visa exempt, after which a tourist visa OR a lengthy absence from Thailand is preferred.
Unless someone spends less than 30 days in country, with no extension, stays away for a couple of weeks then returns on visa exempt and spends less than 30 days on that second trip. That second method would be unlikely to raise any eyebrows at immigration.