I haven't made any references in over 6 years. |D
I'd really like to start creating refs again eventually though. I have so many characters that need new refs.
Something I have recently begun to do. But mostly it's sketches, nothing too finished. I also practice turning them into pixel art sprites as well, usually in one simple pose.
I did for 2 of my main characters, and got too lazy to continue for the other 3 xD;; I do more like what was mentioned earlier, and usually ref recent pages. And even then, that's more for minor characters. The main group i know well enough to draw from memory xD
well I mean.. that was the plan... sadly I didn't get past the 2 main characters D: I really should make character sheets.. I'm introducing quite a few new characters so I should hop it..
I don't have proper character sheets for my characters because I have so many of them and they change outfits quite often. Instead I have quick sketches of all the outfits and colour maps that I use instead. I've also had most of my characters for a long time, so I've gotten very used to drawing them by now, so character sheets don't really feel like a necessity to me.
References are useful when there's a lot to remember but I don't think in comics they need to be as detailed as say, in animation. Especially if there's only one artist and it's you.
I didn't do any. I'd probably gain time if I did. But I'm still evolving with the design of my characters so it will wait until I've found their permanent appearances.
And more: they'll frequently have changes of clothess so...
ha! no.
i used to have character sheets for my two MCs, but as my style and their designed evolved the character sheets would fall out of use and need updating, and i didnt really need them anymore. other characters will get a sketch or two before i get to work on them, and therell be various references to hand, but nothing as formal as a character sheet.
No but I actually need them.
I've made simple refs, so they'll be sketched full body with a coloured headshot to get the colours right, I felt like my characters will be changing clothes a lot so I didn't bother (Edit: made like a sheet with possible character outfits but even then they're just sketched). The problem now whenever I want my ocs commissioned or I'm doing a trade I don't have a set ref to send to the artist so I compile panels from my comic and hope that's enough.
I'm actually making better reference sheet right now.
I only do charasheets when I'm asked explicitely for them, otherwise... nope O_o" It stops me frim drawing on my manga... quick scribbles/outtakes/etc inbetween, okay, but I personally don't see much of a point in charasheets oo
I'm also no friend of long descriptions of said character next to the charasheet, I love finding all that stuff out in the story itself =)
Not unless I want the character drawn by other people.
But for my own reference I just go back to previous pages.
I only have one reference sheet, and I really should make another one, cause I can't continue looking back at older pages as references XD
I do character sheets, backstorys, and a short story for each character in the book I'm working on, but do none of that for my short stories.
My reference sheets are only for major recurring characters and tend to be little more than a quick basic front on drawing to get the general shapes and then colours dotted around so they're consistent and then a height guide. Given 90% of The 1st Rule characters wear a uniform outfit references for each character aren't generally needed.
I do one for every chapter pretty much. I use them for clothing, since they change their clothes a lot, and one specific character does their hair different a lot as well. They also function as my palette. 
Ah, after reading through some of the other replies, to add onto my own:
while I don't really do outfit/pose reference sheets for my chars, I absolutely use the heck out of Photoshop's color library things. I have one of those for each character to keep the colors consistent and be able to reference them quickly. If I didn't have access to that tool, I would def have to have a ref page of some sort to color match off of.
I'm cant' say for EVERY character but at least the majority
doing a reference sheet is a good way to see the character and their design/style. most of the time if i wasn't redraw them ill do a character sheet but other than that ill be too lazy and just draw them in an illustration/ concept way instead.
I don't have any. I only did the "they look like this" sketch once, then changed it once and that's it. I even chose the colors during the first chapter!
And for a few months now I'm trying to make a new reference sheet, but I know it is useless now, because this guys will be older in just 3 chapters. So of course I sometimes forget small things like the patch on main hero's forehead, next day I come back to this page, draw it while I'm cursing... 
So, i think, it is not so necessary, if your characters don't have any really complicated design.
