#1. It opens up more opportunities for Edge post-WrestleMania 37

We're not sure how long Edge's current WWE run will last. Given that he's a part-time legend, the assumption is that he will only stick around till WrestleMania and may come back by the summer at the earliest.
Even if that is the case, turning heel can open a lot more doors for Edge. While he could feud with certain top heels on the roster, it makes a lot more sense for him to be a heel and help elevate younger babyface Superstars.
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One could argue that it doesn't matter whether Edge is feuding with a heel or babyface as he has transcended any such label for his character. While that's partly true, it's always good to help elevate current babyfaces.
Many WWE fans feel that the company doesn't handle babyfaces as well as they used to 15-20 years ago, and only Superstars like Drew McIntyre are among the exceptions.
Either way, Edge could start facing a lot of younger babyface Superstars at big pay-per-view's going forward if he turns heel.