I used to keep them, but back around 2008, my mom made me throw them all away When I recently acquired some old sets, I did keep the boxes. I have the boxes for the Tarakava, Manas, Bahrag, all 6 Bohrok-Kal, the Toa Terrain Crawler, Ultimate Dume, Piraka Stronghold, and some of the othe playsets. I have also held onto all the 2015 and soon to be 2016 boxes.
I started collecting in 2004, and I surprisingly bought al of the sets as they were released. I have no idea how I afforded them as a kid. But, now that I have a paying job, I was able to go on eBay to get all of the sets I missed out on from the early days.
Biggest mistake I made was not buying Toa Mata Nui when I saw him in stores. I had all the other 2009 sets. I don't know why I held off on him. Let's just say it put me back around $130 on eBay.
It got to a point where I had 85% of the sets, so the completionist in me was like, "Let's go buy the rest." I don't know, I'm happy. I love having the entire collection all built up and in fairly good condition.