what's the purpose of a bay leaf?

A fresh one can, they are really aromatic. Problem is, most are old and don't do or add much.

Bay leaf is a seasoning, just like pepper or rosemary. It has a distinct flavor that is desirable in many dishes. One bay leaf cooked with a pot roast makes a noticeable flavor in the finished product.

Yes it does make a difference.

I have a bay leaf tree. I find if I saute' fresh leafs in olive oil before I use them, it brings more aroma and flavor out.

Cook 2 pots of rice. One with a bay leaf, one without. Tell me if you can tell a difference.

They are too expensive at the store, but I love the flavor. So I just grew my own tree, the fresh leaves are night and day better than the store bought bay. A tree costs about $20, which pays itself off quick if you use them a lot.

Fresh bay leaf can help a pot of red beans. That's all I ever use it for.