A template allows you to have a base document that contains all of your static content so you don't need to recreate it each time, along with style and swatch defintions that you want to use, Master pages, layout, and so forth.
The only functional difference between a tempalte and an ordinary document is the default behavior when the file is opened. Documents open "as original" and templates open as an untitiled copy to prevent you from accidenatlly changing them and saving over the template itself.
You can actually convert from one to the other by changing the file extension.
I'm setting up a quotation document for my florist business.
Never used templates before.
What's the difference between saving as an ID template, or just setting up the document and filling in the details with different figures every time I do a quote.
What are the benefits of having a template?
Opening a normal ID document and changing some content, then saving it to its original name with File > Save, eventually makes a file prone to corruption. To avoid the risk of corruption, save each document with a new name, using File > Save As. Opening a template creates a new untitled document; the first time you save it, ID asks you to name it, so you're not re-saving a document in the risky manner.