Like @Sysm said above there's a whole bunch of cons with no pros. There's 0 benefit to upgrading besides "look we're fully upgraded". I could make a con list for days but just off the top of my head:
Annoying as fuck browser notifications Ugly UI where you can't even find anything Ruined threads because their support for BBCode seems to be screwed up Next to impossible to embed anything in posts because their embedding system is just that bad etc, etc, etc