Hello Shashank
In response to this, take a look at this post.
Remember that BGP’s primary function is to share prefixes between AS’es while IGPs are used to share prefixes within an AS. Now if you have a prefix within an AS that you want devices in other AS’es to have access to, then this is the prefix that you should advertise to iBGP, which will in turn advertise it to other AS’es via eBGP. If you have prefixes that you don’t want other AS’es to access, then you don’t need to advertise them to BGP.
So the criteria to use is “do I want a host in another AS to access my prefix?” If so, then advertise them, if not, then don’t.
I hope this has been helpful!
Laz