You're consolidating and/or cleaning up your list of Preference Sets, and you're wondering what will happen to projects (LFX files) and drawings (DWG) files that were previously referencing those settings.
When a Preference Set is associated with project, only the name of the Preference Set is saved. This setting makes it easier to restore a project between office and home, or client and tech support. In these cases, you'd just need to name a new Preference Set exactly the same as the original one.
At the same time, if the designated Preference Set is not there, it will switch to the first in the list. So you'll need to take a couple of important steps before cleaning our your list of Preference Sets.
Step 1: Back up!
First and foremost, back up all your existing Land F/X projects (including templates) and Preference Sets. How to back up projects and Preference Sets
If necessary, you can always restore existing setups and keep going with the look you'd started with on a given project.
Step 2: What is actually in the Preference Sets you're about to clean up?
Determine why you had so many Preference Sets to begin with. Remember, the Preference Set should be the single item that keeps and holds your standards for the office, such as text styles, layers, colors, callouts, plant sizes, and schedule defaults. Although you can create as many Preference Sets as you need, too many of them can lead to a situation that's difficult to control.
As an example, when you add plants to your project, the plant data options (user fields) are created from the Preference Set that was active when you are or were in that project. If you delete that Preference Set and start a new one while you do not have the same user field options set up, new plants you add to your project might have different settings for these options, making them inconsistent in the Plant Manager and Plant Schedule with plants that were already in the project before you deleted the Preference Set.
Compare what is so different in each of your Preference Sets. Because your Preference Sets hold so many of your standards, it's crucial to keep these settings consistent when consolidating your list of Preference Sets. Your office might also have different Preference Sets for different clients or types of clients, project types, agencies that are involved in your projects, etc. Each of these Preference Sets might be holding a whole different set of standards for those situations, so keep this possibility in mind as well.
After you've backed up all your data and figured out what is in your Preference Sets and why, you should be in a better position to delete the Preference Sets that are obsolete, redundant, inconsistent with your actual office standards, etc.