Excellent question, and one that I've actually been eager to post an answer for.
First, SlickEdit's wildcard project support is dynamic. Maybe too dynamic -- if I had time to redesign it, I would dial it back. What does this mean?
1) When you start SlickEdit, or when you open a wildcard project/workspace in SlickEdit, it does a file scan at that point to find all the files matching your wildcard specifications.
2) When you rebuild your workspace tag file, it does a file scan to find the files matching your wildcards.
3) When you do a build, or when you do next-error or double-click in the build window to go to an error, it may have to do a file scan to find the files matching your wildcards.
4) A multi-file search of your workspace or project will also trigger a file scan to find files matching your wildcards.
5) Closing and re-docking the Project to Files tool windows may trigger a file scan to find the files matching your wildcards.
The assumption was that it is easy enough to create a project and add files using "Add Tree", and also pretty easy to add new files as you go along, so if you are using wildcard projects you want a whole other level of dynamic behavior, and that is what wildcard projects attempt to provide. There is no realistic, cross platform (and file-system independent) way to know when new files pop up in the project directory tree, so we attempt to get a fresh list whenever we need it.
Normally, this is no big deal with small projects, we can get a file list very fast. And those are the sort of quicky projects that wildcards were intended for. However performance neccessarily breaks down when you put the source code on a remote file system or cross the 10,000 file boundary (that's not a real boundary, 10,000 files is just the line between having a lot of source code and having a silly amount of source code).
13.0.1 is going to add more in-memory project file list caching. This will improve performance dramatically for certain operations for all project types, but especially for projects with wildcards. However, it will not improve performance for initial startup and initial project/workspace open, which, with a wildcard project will still require a file scan.
Recommendations: unless your projects are under 1000 files and on local file systems, if it is not too much of an inconvenience, replace the wild cards with Add Tree's, and let the project file manage the file list.