This is the Save option to save a design, technology, profile or symbol with an existing filename, the information is saved without further prompting. If it has no filename e.g. if it was opened using the file import mechanism or New, then the Save As dialog is automatically displayed prompting you for a filename.
When in a Schematic design, you can use the Save All option to save all changes in all sheets and blocks within the current design.
Shortcuts
Default Keys: Ctrl+S
Default Menu: File
Command: Save
Default Keys: None
Default Menu: File
Command: Save All
Locating this option
Available from: File menu > Save option
Available from: File menu > Save All option