Comment by rolph

unless you alays have your email open on your device, its a tiny PITA to fire it up, login, remember your issue, and compose a proper message.

so when you [@user] tag a user rather than email its kinda like a rhetorical question, your not expecting a reply, but if someone just happens to pass by and notice your tag, they might answer.

also @user might mean wasted desire to some, but other users here might see a previously agreed upon heuristic is in play, and act in that context.

for example if someone from a very small subset of usernames that i recognize, were to @rolph me, i might SMS them at a previously agreed mobile number, if i see the signal in a reasonable time.