Travel information in Tibet is very fluid and the situation can change quickly, but if you are wondering if you can travel freely in this area, the answer would be that probably you can. It is true that besides a Chinese visa, a permit is also required for you to enter the TAR and there are also many places where lone foreign visitors are prohibited from entering. Nonetheless, many individual travelers have found ways to travel relatively freely throughout Tibet and many of them have been enjoying this freedom for years.
Of all the Tibetan areas in China, the TAR is a special case. Along with a visa, foreign visitors are officially required to have a permit issued by the PSB to enter the province. Without it, you'll be unable to buy air or bus tickets. However, you don't have to worry about where and how to get these permits. If you take common routes, such as Chengdu - Lhasa (Air), Golmud - Lhasa (Bus), etc., foreign travelers must buy both the permit and the ticket together through a travel agency.
In China, there are open and closed areas for foreign visitors. Unfortunately, most areas in the TAR are closed. If you want to go to the closed areas, you need to have the local PSB near those areas issue an 'Alien Travel Permit' showing your destination. The availability of these very much depends on the situation at the time. To find out, either ask the PSB directly or gather some information from your fellow travelers. In case you can't obtain a permit for yourself, the other option is to charter a car through a travel agent. Using this approach, you can get permits for many of the closed areas, except some of the more sensitive border areas. In Qinghai, Gansu, Yunnan and other areas outside of the TAR, many Tibetan places are open to foreigners.
Alien Travel Permit
Alien Travel Permit
In most cases, you can easily reach the restricted areas when there are bus services running. In case you do turn up in a closed area without a permit by mistake you should be aware that you are breaking Chinese law and that you are all right as long as the PSB officers don't find you.
If you are found in a town where there is no PSB foreign affairs section, your case might end simply by presenting your passport. In towns on a highway where foreigners often pass through, you are usually requested to move to a hotel designated by the PSB, even in closed areas, there are towns with designated hotels for foreigners on package tours.
In restricted areas, you are frequently warned not to take photographs. Even if you didn't intend to enter a restricted area, you should be careful.