When using parallel clamps, we stick two pieces of wood together with till it dries. The primary purpose of these clamps is to hold the pieces flat and even. We stick it together and secure it with clamps to help it stick and also create a nice even surface for your projects. However, gluing up non-parallel panels is tricky as sticking the clamps in the wrong place can disrupt the balance and cause it to break. But yes, you can use parallel clamps for non-parallel panels. The thing you need to remember when using it is that sticks the clamps where the glue is and has something under to rest the uneven ends.