What is the reason behind reviewing NHL major penalties, and how has this affected the Stanley Cup playoffs?

In Game 1 of the Minnesota Wild-Dallas Stars series, defenseman Matt Dumba of the Wild made a hit against Dallas forward Joe Pavelski that resulted in Pavelski hitting his head on the ice and being placed in concussion protocol. Although no call was initially made on the play, a major penalty was later assessed to Dumba. However, after a review, the penalty was reduced to a minor penalty for roughing. Similar situations have occurred in the first round involving other players. The NHL rule for reviewing a major penalty is covered under Rule 20.6, which states that referees must review all plays resulting in a major penalty (except for fighting) to confirm or modify their original call on the ice. The referee has the option to confirm the original call, reduce the penalty to a lesser penalty, or rescind the penalty altogether after video review.