It could be a very useful tool if you have more than one profile -- say, if you maintain a personal one, another for your business and yet another for your celebrity pet. On the other hand, it could be a privacy nightmare waiting to happen, seeing as a bad actor could gain access to all your accounts if they get a hold of your main's username and password. It's probably best to switch on two-factor authentication if you take advantage of the feature if and when it launches. Part of the code reads:
"Quickly and securely log in to all of your Instagram accounts with one ID and password . . . Make one of your accounts your main account and use it to log in to all of your other accounts at once . . . Your accounts will remain separate but logging in will be fast and simple . . . Anyone who has the password for your main account will have access to the accounts connected to it."
In addition to a quicker log-in experience, the feature might also make Instagram's login platform more robust. It could become more like Facebook Login and could carry over more of your profile into the apps you use it with. Account Linking is still in its very early stages, though, so it'll likely see more changes before we officially hear about it from Instagram itself.