You can only Save once you have changed something. This might be adding a new entry, editing an entry or moving the position of an entry; something that changes the content.
When you press Save one of two things will happen depending on if there are any Write Plugins selected [Plugins]
The image below is an example of the Save Preview for Example Library 1 and 2 loaded with the "Add Boo!" example write plugin selected.
This is the chance to check that what you are going to write out is what you expect to be written out.
If you choose to overwrite a file then a backup is made of the older file. That way you can always get back one step if things haven't gone to your liking.
The back file is time-stamped.
For example:
Saving as a filename of "Save Example.msp" and then some time later overwriting that file will produce a backup file with a name similar to "Save Example - Copy - 2020 Jul 23 04-03-40.msp" where the syntax is "{name} - Copy - {yyyy mm dd hh-mm-ss}.msp"
Wiki: Normalise Intensity Plugin
Wiki: PQI LIMA Plugin
Wiki: Plugins