It likely depends quite a fair bit about the organization of your work. It would, of course, be best to write clearly, make special notes about certain approaches, and make comments about the solution (check the units and why it the result makes sense). If you do these things, your solutions might be useful to look over later. If the solutions are a mess, keeping them is probably worthless.
I think it's worth it to keep your solutions. So much of physics builds on basic principles. The further you go, the more often you will need to refer back to the fundamentals as it is often necessary to refer back to the solution of a simpler problem to tackle a more complex one. And like Physics Girl PhD said, it's worth keeping good notes.