Why do we create mapping in elasticsearch while setting up repository?

Question

Okay, I got it this question that what is the need for mapping.

Now I am going through a piece of code, what they are doing is that they are generating the mapping while creating the elastic search repository by pushing a dummy object and then deleting it.

I got it that elastic search can generate mappings, but what is the point of doing so. It does not help with the search queries ( at least the regex one that I have tried unless you explicitly tell in your mapping that this is of type keyword).

I would be thankful if someone can explain this.