Depends how intensive the game is. For the majority of simple rpg esq games you don't really need it, or can at least get away with other timing methods. But if you expect your fps to dip below or above your target then you should idealy do so.
QFE.
If you're writing something in which all the hardware will be the same, it's not as essential. (EG, Consoles, Handhelds, Etc)
If you want to have your software play correctly on as much hardware as possible, it's basically required. Try playing quake (Frame based updating) on todays hardware. Runs as fast as you can render it. Means the game is incredibly fast on todays blazing processors. Play a game such as Unreal Tournament on todays hardware, runs just as smoothly as it did then.