Well, even if I am somewhat favourable to this feature, I can name a few: Encounters were not designed to have this kind of flexibility, wich can make some runs easier than intended, and it gives an advantadge to hybrid classes wich now have the added utility to swap roles.
Example:
- With this feature, in a raid a warrior may be preferred to a rogue because while doing slightly less DMG, you get an instant additional offtank when required.
- Bear run in Zul Aman: the difficulty is set to having a tight and closed group with no time for in-raid spec changes, with this feature it will be FAR more easy to get a succesful bear run with a far less dedicated composition
But again, this issues are really minor and very high end focused compared with the benefits it givres to whole server, I think.
And no less important, it is an income source for a team that otherwise is receiving 0 money for medivh, and well… I want my server to be also loved and desired for the devs.