Bitelon is a fairly standard monster with a decent attack and a piercing effect, but its convenience lies in the fact that it's a 6 star monster. You can tribute summon it easily if you have a monster on the field, or special summon using cards like Big Wave Small Wave. Or make it work in a high level monsters deck using Mausoleum of the Emperor.
Bitelon has low defense, which can be easily taken advantage of by your opponents since position switching cards are common. Spikeshield will bump up Bitelon's defense all the way to 3900. And Spikeshield on its own is already a useful defensive card that you can use with most monsters, making it a good fit in a lot of decks.