Some puzzles are only made to complete once. After spending hours and hours on them, you may not have the energy to put them together again in the future. Or, they may be so gorgeous that you can't stand to see them packed away in a dark box for months or years.
When you are looking to frame your puzzle, there are many alternatives for keeping it together. While some prefer to slide it directly into a frame, this usually isn't a great choice if your frame is bigger than the puzzle as it may slide and shift about, causing breaks. When this happens, it's best to grab some glue and stick all your pieces together.