I read somewhere that in some states it's actually against code to bury cables in drywall without a box or access. My cousin's an electrician and he said if the customer refuses an access panel, he just walks away from the job. It's one thing if you're fishing a temporary line for a TV mount, but full on sealing it in the wall is just asking for a nightmare five years from now when that cable goes bad. People don't realize how much of a hassle it is to cut back into drywall later, especially if you forget exactly where the cable runs.