Shared Usernames

The main issue I would say when having separate profiles as couple is it compromises your visability as a couple if someone uses the search engine to find couples, regardless of whether you have it written in your profile that you're a couple with @a.nother it will never reach some that are only looking for couples.
I'd always recommend any couples that operate with singles profile to have a couples profile too as it cover all bases.
But as always it's completely up to the people involved how they wish to do things.

Mr Bump