I have done it when we have rubbish cleanup ... one man's trash is another man's treasure.
I usually fix stuff up for the kid's mates.
The best score I every got was 20 intact PC's from a community college for free. I arranged with a mate who was a deputy principal at a local public school to pick the lot up in a trailer, took them home and reformatted the lot and blew out the dust, then delivered them to the school the next week.
They put them into the grade 1,2, and 3 classrooms for resources for the primary school kids.
Just basic stuff ... but it was nice to see them getting used instead of going to the tip.