I consider myself to be a loose collector. But what I found when trying to complete the later years of the ARAH line was that MOC figures were often no more expensive than loose/complete ones. So I have managed to accumulate almost 80 MOC Joes - all from 1992-1994 - that don't really fit into my collection per se but I don't have the heart to open them.
I also have found myself accumulating boxes for vintage vehicles. I only own maybe two ARAH vehicles MISB, but I have a TON of boxes to display with loose vehicles. The art is too cool to pass up.
When I buy the newer stuff, though, it all stays MOC/MISB unless it's something that really attracts my attention. I army-built several of the Cobras from the 25th line, so I opened all but one of each of them (what good is a MOC army?) and I bought extras of the VAMP and Stinger to open and display with my VAMP collection but the rest of it is MOC. Ditto with MOTU Classics and the 20XX MOTU line and any other new lines I dabble in.