[color:"orange"]so it's kinda for beginners...or is it cheating??[/color]
Generally they are used for cheating, but also have valid uses. There was a trainer for Diablo (IIRC) that allowed you to backup and restore characters. The game put part of the information for each save in the registry, which meant you could not easily move your save to a different computer, or restore saves if you had to re-install windows.
Some online multi-player games store character data on the server, rather than your own hard drive, to reduce cheating. If the server has any problems, though, they can leave characters susceptible to corruption or deletion, and there are some trainers to backup and restore character data.