As with the auto-attack. with it on ... Allowing the freedom to send messages without completely hampering game play.
I think this is primarily why it should be beneficial. I don't think there can be a situation where, from a gameplay perspective both systems (auto-attack on/off) will be completely equal. One approach will end up being the better approach, and everyone will end up using it. However, as a means to communicate during the fight without having to stop the fighting completely this kind of addition would work just fine.

Even better would be if they could make it so toggling it on and off would complement the other. I mean that they could make toggling it on or off a gameplay function with ways to approach situations differently. If they aren't in a direct competition between each other (as in both are used to accomplish the same thing) their co-existence and relevance would be better ensured, instead of one approach becoming useless after a while.

Not 100% sure what you refer to on Tags so I am sorry. still very new to Forums.
To make the community team and the developers to read this thread, you need to put a "tag" on it (in this case dev1022, which I can add at this time it seems). The tags are found in the "In Development" forums. If you want to post a thread related to some of the features in the In Development, you should add the proper tag(s) so that those who should notice the thread will!