Ask HN: Why should I apply to a start-up accelerator?

Fellow HN:ers.

Thru my alumni-network I have got the chance to apply with my start-up idea to an trial start-up accelerator.

At first I thought it would be a great idea; but the more I work on my application the less sure I am.

To those of you that have been in accelerators like YC; what was your main motivation for applying and what did you hope to gain?