It's important to be able to have your work piece held by some kind of vice when you're working with it. It really is very helpful in order to have both hands free to do everything that you need to do when you're soldering. What we use are these different types of vices to hold our work piece.
I have a couple of examples here. This is the first one I'd like to show you. It's a Pan vice which allows us to manipulate the part in different orientations that makes it more convenient for us to work with. For example if we need access to both sides of the board we can tilt the board up on edge and have access with both hands from either side.
For some smaller boards it may be possible to grip it from the edges like this, and for that you might use a vice that has a wider jaw. If you're working with something that is very, very small, it might fit in a vice like this, so it's nice to have something with a wider jaw.
And finally, for large parts, you run into the problem where the board begins to flex when you apply pressure, so in that case it's often helpful to have two vices handy so that you can clamp it from both sides. In this case we have a lot more force that we can apply before the board bends and flexes. So sometimes it's helpful on a larger board to have two vices.
So just to reiterate, it's important to have something to hold your work piece so that you can have your hands free when you're working with a soldering iron and your solder.