Time Jacker
Loving YTtalk
I keep everything. You never know when you might need them. what if YouTube disappeared tomorrow? What would that mean to you? If you're not keeping you're files, you have to work under the assumption that you no longer own them or have access to them.
The best thing to do would be to buy an external hard drive. It doesn't need to be an SSD; a plain old mechanical HDD will do. They're so cheap now and you can get multi terabyte ones for dollars. Archive them off to your external drive and forget. For really important files, you might also want to consider doubling up with something like Dropbox too.
Finally, keeping your files archives will not slow down your computer. Moving them around, deleting them, editing them, adding to them; all of that has the potential to slow things down over time. But leaving them all in one place and forgetting about it is all good.
The best thing to do would be to buy an external hard drive. It doesn't need to be an SSD; a plain old mechanical HDD will do. They're so cheap now and you can get multi terabyte ones for dollars. Archive them off to your external drive and forget. For really important files, you might also want to consider doubling up with something like Dropbox too.
Finally, keeping your files archives will not slow down your computer. Moving them around, deleting them, editing them, adding to them; all of that has the potential to slow things down over time. But leaving them all in one place and forgetting about it is all good.