The settings under External References look very simple and unimportant, however, they can significantly affect the performance of opening and saving large assemblies.
Open referenced documents with read-only access, when you open an assembly as read-only, the component files are not opened read-only unless this is selected or the files have already been opened by someone else who has to write access to the files. It is a good idea to have this option selected. If not, when you open the assembly, you get write access to all the component files, even if you have no intention of making any changes to those files. This prevents other people from being able to change these files.
Don't prompt to save read-only referenced documents, if you select the option to
Open referenced documents with read-only access, you should also select this option. If you do not, SolidWorks will prompt you several times for each component file when you try to save the assembly. In a large assembly, this can be very frustrating and time-consuming.
Load referenced documents, this option determines if documents that are referenced by components in the assembly should also be opened. Selecting
Prompt will ask the user if these files should be opened when the assembly is opened. Depending on the stage of development, selecting
Prompt is usually a good choice as it allows the user to only load references as necessary.
Search file locations for external references, this option turns on the search of the file locations listed in the
Referenced Documents list. This option should be cleared except when specifically trying to locate files that have been moved improperly. Leaving this option selected can cause a significant increase in file opening time if there is a long list and file paths.