It's hard to convey just how important knowing how to make patches really is.
We can look at an issue queue and see all sorts of feature requests and bug reports. Some may have detailed suggestions of how to do a feature or even have code pasted into the comments that worked for one user. Some bug reports or follow-ups may have the problem identified down to the line of code.
But imagine that we made this module because we needed it, but we don't need the suggested feature or haven't run into the reported bug ourselves.
When a feature implementation or a bug fix is in the form of a patch (or code we can pull directly into our repository), it makes a huge difference.
First, people other than the module maintainer can test that patch and confirm that it, precisely it, and not a hand-edit approximation, works.
Second, the maintainer herself can just apply the patch and not really touch the code at all.
By using the issue queues and patches appropriately, all the work of fixing or improving the module, theme, or other project can be done without the maintainer's involvement. This can easily make the difference between an issue remaining open for years and a new release coming out with the fix or feature we want!