Welcome to the site! I agree with Billy, the Simpsons avatar is cool.
Personally, I don’t add my duplicates to my collection. I don’t have a ton of them really, but I keep them physically separate from my normal collection. They are stacked in a shoebox. I am keeping them to give to my son when he is older to jumpstart his collection if he ends up liking cards.
If I have a duplicate of an insert or a cool rookie, I give it to my brother. Otherwise I will look to trade it with someone here. I will trade commons sometimes if I have something someone might want. I’m not a big trader, as for better or worst I am not very trusting. Other than one other person, I have only traded with Billy. But I’m sure most here can be trusted, at least the regulars for sure. My brother just moved to CT though, so not going to be as easy giving him cards anymore.
Before I found this site, I donated a bunch of common duplicates to Goodwill.
Keep in mind, this is just what I do. It seems like you like to keep your duplicates. I like the clean look of just having one of each card, and I don’t have much space to keep my collection a it is.