According to analysis by Mark “Murch” Erhardt of Chaincode Labs, 88% of all Bitcoin transaction inputs pay higher fees than are necessary. Erhardt bases his conclusion on data showing just 12% of transaction inputs use the SegWit format, which is less fee intensive than transacting with legacy inputs.
Erhardt believes that a reliance on legacy transaction fees keeps Bitcoin blocks smaller than they could otherwise be, contributing to a seemingly growing backlog of unconfirmed transactions.