The Snippet glossary is a place to store reusable expansion snippets

Imagine you have a glossary with 1000 letters. Each letter starts with your letter head which contains your address, phone number, logo, etc ...

Do you want to hardcode this letter head in all your entries? If your address changes you will have to edit all your entries. If you have your letter head in a a Snippet and reference that Snippet in all your entries, all you need to do is change your Snippet entry, and all your entries will reflect the change.

Another possible use: imagine you have trouble remembering that Control Shift Left and Ctrl Shift Right resp. select the previous and next word, create the following Snippet entries:
select_previous_word => {Ctrl Shift Left}
select_next_word => {Ctrl Shift Right}

And then you can reference them in your entries where you need those selections:

{Snippet}select_previous_word{/Snippet}{Lowercase}

It can make your commands more readable.

Snippet Glossary