That's a really good question, especially since I don't exactly shy away from first person.
So, I suppose, the real question is more along the lines of "Why do I think you shouldn't use first person?"
Well, okay, it's not that I think you, the specific you sitting here reading this post, shouldn't use first person; it's that I think the general you out there shouldn't use first person. At least not until you have figured out how to write in third person. First person, especially for the beginning writer, has too many traps and short cuts; until you know how to get around them, you should write in third. And, actually, it's writing in third that will help you to learn to avoid the snares.
So let's start with descriptions...
* * *
Do you know the drill, yet? I feel like you ought to know the drill. Unless this is your first time here, in which case, here's the drill:
His name is Bit, and he's glad to meet you.
Seriously, though, hop right over to Indie Writers Monthly to find out why you ought to be writing in third person. Or, at lease, why you shouldn't be writing in first. No, they're not the same thing.