I haven't filled them.
I've transferred about 40 drawers worth of stuff from old metal units that I'm going to bin and kept my existing plastic ones (the small grey units of which I have 9 in total). I have 40 or so of the new thin drawers still empty and 10 of the new larger drawers with nothing in them.
What I have been able to do is spread stuff out so that if an army only fills half a draw I can leave it at that and not need to fill the space with other stuff which is what I was doing up until now because space was at a premium.
Even when each drawer has something in it (and that won't be for many years I hope) I'll still have 'compression' room where I can start doubling up again and filling in the gaps.
I've pretty much reached a stable amount of stuff any way. I've noticed that I get rid of armies and scenery now as I complete new projects and I lose interest in the older things where previously I kept everything.
Time will tell
