it could be disorientating to have your active character constantly snapping around.
It's switching around now, constantly, anyway. This proposed change just eliminates the manual labor and the disorientation you feel when you go to a PM/RP/Chat from your notifications or otherwise, start typing, and then realize you are on the wrong profile. (It can also be unintentionally revealing when you go to a chat and start typing, or even post, but you post from the wrong profile.)
In my case, this is a constant thing! I go to a PM, I need to switch to reply. I go to an RP, I need to switch back to reply. If I closed that PM, and someone just replied, I'll need to switch again after I open the PM, so this time I won't close that PM tab, for sure. A feedback notification pops, and that's another profile swap if I want to reply. I search recent chats and see activity in a chat I frequent, but that means another manual profile switch when I open it up. Oops, back in that RP I'm on, it popped to a new page, or otherwise endured a page refresh. Need to do another profile switch there, which will set up the next switch for the next thing I open up. (So, potentially, after this change, even page-refreshes end up keeping you on the correct profile, regardless of currently-active profile, for a page that gets refreshed.)
(BTW, all these profile switches are why I end up with 10 Lit tabs open in my browser, so that the need to manually switch is reduced.)
All these switches are manual steps that often must be performed before posting on a newly opened page that hopefully will all get eliminated if this is fully implemented.
To me, it's worse/more-disorienting now. I have no problem with adding in configurability, though. Go for it!