Yast patch type in Online Update

When starting Online Update the Show Patch Category shows by default :“Needed Patches” and these are the ones I apply to keep my system up to date. But I then noticed that if I change the Show Patch Category to “Unneeded Patches” that there are quite a few updates there I could apply to my system.

What is the difference between “Needed Patches” and “Unneeded Patches” and how does Yast determine what update is needed or unneeded ? Will applying what Yast determines as an unneeded patch do any harm to my system ? Shouldn’t all patches be applied to keep a system up to date ?

**Unneeded Patches

**Patches that either apply to packages not installed on your system, or patches that have requirements which have already have been fulfilled (because the relevant packages have already been updated from another source).

ie. You don’t have the application installed that the patch is designed for and/or you have installed it from another source (such as Packman and that version supersedes the patch level).