In my last job I got fed up with my 4 drawers of "reference" material (accumulated over 20 years) and purged it over about 6 months. By the time I'd thrown away all the stuff that was no longer relevant, had been replaced by later documents, was saved on my computer or the intranet, and things I was clearly never going to use, I reduced it to about 2 drawers full. Half of that I switched to ring binders which sit on my shelf and are much easier to find stuff I need, leaving me with only one drawers worth of filing.
In my current job I am delibrately keeping it to one shelf of ring binders and one filing cabinet drawer. But it depends on just how much you NEED to keep for reference.