#1 Opening up of different possibilities

Brock Lesnar's victory at Extreme Rules 2019 has opened up a plethora of possibilities for Raw as a whole.
Despite the proven qualities of Seth Rollins as the face of the brand, his Universal Championship reign was turning out to be underwhelming. His feud with Baron Corbin did not help his cause as the fans were simply not interested in investing their time in it. The situation got even murkier with the involvement of Rollins' real-life girlfriend and Raw Women's Champion, Becky Lynch, in the story line.
Hence, things needed to change and the best person to bring about that change was Brock Lesnar. This now gives an opportunity for WWE to press restart on a number of elements.
Seth Rollins may get the required time to reclaim and regain his spot as the top babyface of the company with a fresh approach. The involvement of Becky Lynch has most probably been taken out of the equation as well.

Furthermore, WWE may also push another wrestler to feud with Brock Lesnar. A good quality feud with Lesnar has always been a sure-shot way of establishing the legitimacy and credibility of any wrestler, be it Daniel Bryan, AJ Styles, Finn Bálor or Seth Rollins himself.
Hence, WWE might think of pushing a fresh wrestler to feud with Brock Lesnar. The most immediate choices for that would be Braun Strowman and Bobby Lashley, both of whom have established themselves as credible challengers through their recent feud.
Possibilities are aplenty and it is entirely up to WWE on how they capitalize on it. After all, Brock Lesnar is one of the best wrestlers ever to set foot inside the squared circle.