I've done a lot of scrapping (large appliances, electronics scrap and such), and have trash picked a bit (I use to repair electronics, so would fix / flip things, still do if it is something decent). I've only done a little "dumpster" diving, but can get in trouble for that and told to leave very fast since it is usually private property / no public use of dumpsters. I've gotten some great stuff though both dumpster diving and trash picking, were talking items with reasonably high value, just items that are broken and I simply had to repair, or considered old and tossed out (but still valuable). As mentioned, the larger eviction style cleanouts often net the best stuff, or simply people moving and down sizing.
People that have never trash picked of any kind, might be completely shocked with what gets thrown away, sometimes some high value stuff (of course depends on what is considered high to you).
And I'm sure the bed bugs comment will scare many people off, but it isn't a problem most of the dumpsters / cleanouts, and it if is, you will see the bugs. I've looked them up just to know what I'm looking for, but can't say I've really seen any in all my years picking stuff up, it just isn't a big problem in most areas, not around where I have been at least. I always stayed mindful, but never worried about this.
Just keep in mind you can get in trouble, while chances are low, and you will likely only be told to leave, it is generally not allowed by most businesses. Some don't care, but others will not allow it at all.
I've done it to get items I can fix up / use, or resell. Saves some great stuff from the dump / landfill depending on where it goes / how it gets processed, but have saved some really nice stuff.
We throw out a lot of stuff that could be sold because quite honstly, the amount it would sell for (or the amount of people we have to chat with and then meet), just isn't worth it. I had some art work that I paid ~$50 for. An air purifer, this cool 'tent' thing for kids. I normally just toss it all up for $10/each (as that's sort my limit for what's worth putting up). If I don't get any replies in a week I throw it away.
I hate tossing sutff and would love to give it a home but if it's not worth at least $10 to someone I guess it's landfill