Custom offer is not affecting the profile it means we should always use gigs . If there is no benefit of custom offer then why fiverr use this.
I use custom offers a lot and they work well whenever someone sends me a message and wants something directly from me with the prices. Usually the buyer will accept a custom offer if they have sent me many messages and questions first.
I use custom offers way more than plain gigs. Since gigs are attached to every completed customer order it affects my profile just like any other.
When you send a custom offer, you can link it to one of your gigs that is related. This will have it show in your results for a gig when you get that great review.