BoxRec

There's a long history of fighters relinquishing belts. But I think the most performative and high profile was the literal dumping of the Apartheid WBA belt by Lloyd Honeyghan in the golden age.

Riddick Bowe famously threw his WBC belt in the trash

Many fighters have vacated a title to move up to the next weight class

I remember there was a unique situation back in 2004 where Tarver was the WBC Light Heavyweight Champion, and Glen Johnson was IBF Light Heavyweight Champion and in order for them to fight each other for what was widely considered the Legit World Title of the weight class they both had to vacate their belts due to not fighting mandatories or something.

Larry Holmes had a tantrum when the WBC expected him to defend against Greg Page and Tim Witherspoon when he wanted to fight the likes of Scott Frank and Marvis Frazier. The usual arrangement was that the no 1 guys would fight for the WBA belt and Holmes would fight second raters. So Holmes vacated the belt and accepted the new IBF belt, who would allow him to go on cherry picking opponents.

The IBF seemed to establish itself by bestowing their belt on people who were widely considered Lineal Champion, but hadn't fought mandatories in a bit.

The exact opposite of what they do now, but you gotta establish yourself some kinda way

Having Larry Holmes who was at the time Lineal Heavyweight Champion carry their belt was a big boost for them and gave them instant credibility. Same with Aaron Pryor who had the IBF belt at 140.