When I was a kid and I got a new set, I would build it according to the instructions, play with it, and then disassemble it and sort it into my brick collection. Occasionally I would get the instructions back out and re-build it, and other times I would kitbash and make random cool stuff.

My parents still have all my Legos from the 90s, including the instructions, and I've been able to rebuild a bunch of the space ships with translucent neon accents. It's pretty sweet and my kids love it.

Lego used to encourage building new things by putting alternate builds on the back of the box, but intentionally not giving you the instructions. Now they do 3-in-1 for certain sets instead, which misses the point of that.