Quick characterization.

Okay, what do I mean by that?

Sometimes writers give a character a specific, recognizable quirk. A little 'tag' as it were, that makes that character always recognizable.

Most commonly, you see this in situations such as comic books or multi-writer television shows. Where more than one writer is working with a set of characters.

So, an eyebrow raised and the word 'Fascinating' immediately becomes Mr. Spock. All old-time comics fans know exactly who says 'Oh my stars and garters!' and pretty much all fans could probably give a good guess as to the source of 'It's Clobbering Time'.

Giving a character a 'tag' makes them stand out. It's a quick and dirty way of making it very clear who it is. For example, in Harry Potter, the house elf Dobby has an obsession with socks. Garish, mis-matched socks. House elf + socks = Dobby. (Which, of course, they forgot in the movie. Mutter).

One easy 'tag' is a substitute swear word. What does your character say when they would really like to let loose an F or S bomb, but their grandmother is listening? I used to know somebody who would loudly declare 'Sherbet' and I have a personal fondness for 'Freaking' or 'Freak you'.

Is it a lazy thing to do? Not really. It's very useful in short stories when you have limited space and need to sketch a character quickly, and adding a dialog 'tag' helps make it clear who is speaking. (No doubt the reason dialog 'tags' are so popular in comics and screenplays is because that is all the writer has: Dialog and cues).

And, of course, if you are working collaboratively, it can help keep a character straight.

Now...I'm going to go mutter some more about Dobby's socks.