If you want to put those commands/tools on the ESRI Toolbar Control then you will need to register them so that they are available for you to choose in the toolbar properties dialog. If you're creating instances of the command/tool classes yourself via code and executing them or making them the current tool via code then you don't need to register them.
Forgive my imprecision! That is kind of the point of my post. My program is a standalone viewer that will never use any external tools or commands - everything is wired directly in code. I am creating classes for the commands and tools (for example MyOwnUsefulTool class) and using them on an ArcGIS Engine Toolbar control by:toolsView.AddItem( new MyOwnUsefulTool( synchronizer ), 0, -1, false, 0, style );
They work fine without the registration code (as far as I can see.) All the right places in the class are being called (OnCreate(), OnClick(), Enabled and so on.) Is there a hidden problem with doing this (memory leaks, null exceptions, COM errors, Demonic possession, or whatevah?) I'll take the time to add them if they prevent problems but I'd rather not have the code if I don't need it. (I discovered by "mistake" that it worked without the code.)