What is the diffrence of not having classic mode authenitcation in sharepoint 2013 by default?

as SharePoint  2013 started to phase out the classic mode authentication. I have a question popping up in my head.

I still see we implement NTLM and Kerberos as the available options for using claims authentication while creating the web application.

so we don't need a IDP provider, is it the default NTLM is used by SharePoint to implement claims.

so if I have to create new SharePoint web app in 2013 and I cant afford extra IDP providers, I decided to go with the default systems what are options available for me.

also when does the identity provides gets enabled in the web application create page.

Any good explanation or reference to a location would be much appreciated...

kukdai