DDO orphan scan is only good if you could probably write a list of 90%+ of your cc. Before that point, it's mostly useless, because you don't know what it's showing you. The duplicate scan is pretty good, though, especially if this attempt is your first true attempt at organising your downloads folder, and you had a few half-hearted attempts before.
I have 2204 files right now, and that's waaay too much. I feel like such a slattern I used to have more than 15000, though. That was probably when I only had up to Pets installed, and that's when I started feeling the lag. I got down to 3000 before Seasons, and now Seasons is lag-free with a slightly aging computer and everything turned to max, even on big or community lots. (This last leg of the cleanout should make that an and/or. Yay!)
I recommend everyone gets and uses the Compressorizer. Don't do a whole downloads folder in one go or you might run into trouble. Divide into subfolders first, even if all you can be bothered to call them is 'section a', 'section b'...
If your downloads folder is a total mess, you may be better off blowing the lot away and starting again. If there's some sort of organisation, you can probably salvage it, even if it's just that most of your files are prefaced by the creator name. Make creator folders, then, inside those, make a CAS and a Build/Buy folder if it's applicable (and a Hacks folder, too, but I don't know of many creators who are so multi-talented... there are some, though )
Then, use a program like JDiskReport to evaluate the situation. If, for example, you have a huge Peggy folder, but hate her stuff and don't use it, what's going on? Or you might see that you have a bunch of CAS stuff when you don't care too much about your sims because your real love is decorating. This also tells you the size of these folders and the amount of files in them. Generally, the size of each creator folder, or each type folder (for example, if you decide to divide by Hair, FA Clothes, Genetics, Kitchen) should correlate to how much you like and use the stuff in it. If it doesn't, why? Look at the biggest files first - do you think they're worth how much space they take up, compared to smaller files you love? If not, delete them.
I've found that if I have doubts about something, I won't miss or even remember it when it's gone. If you have doubts about deleting it, keep it in another folder and try playing with that folder taken out. Build a house, make a family - did you miss something? If so, put it back. If not, delete it!
If you have lots of files without descriptive filenames, put them all in one folder. How many do you have? If it's about 30, I'd go through them in SimPE and work out what they are and rename them appropriately. If it's more, or however much you can't be bothered to deal with, delete them all.
After you've sorted out your CC, you can use less subfolders. I'm moving mine now to function-based folders instead of creator ones. The more files there are in a subfolder, the more I want to get rid of, so that's helping to motivate me
Once you've cleaned out your downloads, try and have some self-restraint! You might think, well, I got rid of all my crappy hairs and their orphaned meshes and recolours, but now I want some more good ones to fill it out a bit more. That's fine, obviously. But if you always hated Peggy and Rose hairs, remember that! Don't go to them! Once you're happy with the amount and choice you have, when you see a new thing you want, try and think: should I delete something to replace with this? If you can't think of one to delete, maybe you don't really want it. But if you still think, after looking for things to replace, that you want it, get it, because you probably do As long as you want it, you'll use it - and as long as you're using it, it's completely worth having!
And once you have a subfoldering system, never fall into the 'well, it's mostly sorted now, what will it hurt if I dump this one little download in the main directory?'. And then I did that once more, and, ooh, just this time 'cause I'm busy, and then again, and I had to start sorting all over again.
There are basically two ways to have a good downloads folder: you can go the 'keep the zips and the pictures, subfolder by use then creator then set then item' and the 'delete everything you're not using or using very rarely and group the rest together by something' people, which is me. You might find the other method better, though it's too much work for too little gain for me, or you might do something inbetween. Good luck (And apologies for my second essay in a week on here )