LTLT long time low temp cooking is useful for any cut of meat.
For large tender cuts like loin, turkey breast etc, LTLT gives you temperature control as the posters above say.
It's not worth it though for tender, small pieces of meat - a thin steak or pork chop for example won't benefit from LTLT.
Usually the muscles used the most in any animal - legs for poultry, brisket, shoulder, and rump for mammals, will be tough from use and have more connective tissue. These all benefit from being cooked LTLT in order to transform collagen into gelatin between the muscles.
Bones add some gelatin to the equation and are especially important for braised LTLT dishes.