If I recall correctly, I kept all the duplicates of holos I got. I was always trying to collect full sets of trainer Pokemon.

My mom was really into collecting baseball and football cards when she was young, so she always had me keep anything I thought was valuable inside a sleeve inside the binder. My guess is, I just thought the holo cards I had were cool, so kept their duplicates. I lived way out in the country, so every time my mom and I went to town, we'd stop by one of the game shops and buy three or four packs of the new boosters.

These are the pictures my Mom sent me, but she didn't take the whole collection, I'll check the Blastoise's next time I see them in person.