The Help files in Microsoft Word include several warnings against putting private information in your fields and forgetting about it. Many uses of Word are not proprietary, so a letter to your grandmother is unlikely to contain a field that leaves you open to litigation unless Granny is one of those habitual litigators, in which case you probably should call her instead of writing.
But the most innocuous of private jokes can be costly if you forget your wit at the wrong time. It might do your bruised ego good, for example, to name a client folder "Stuff_for_XYZCorp_Bozos," but when that folder name shows up in your filename field, your customer might prove what you always suspectedthat he has no sense of humor at all. So if you don't want everyone to know your file structure and the name of your files, don't leave the FileName field in your document when you pass it to outside sources.
Naturally, this problem is compounded if you put your fields in hidden text!
Let's say that you have sensitive documents and you routinely search for hidden text and remove any fields containing proprietary information. Don't forget to look in the Properties box. You add information there so that you can insert certain fields, but when you delete the field, the information you put in the Properties box is still there. This is fine if you want it there, but problematic if your documents might ever be at issue in legal arguments. It would be tricky for someone to maintain plausible deniability about a project, for example, if he or she is found to be listed as manager of that project because you left a listing in the document or template Properties box.
On the flip side, if you want your name associated with a document, it's a good idea to fill in the Properties dialog box as a matter of branding. In my experience, those who want to grab credit for your work generally change these fill-in boxes, inserting their own names, but you never know when one of them will forget!
And if you want to ensure that no one else modifies your fields by accidentor that you don't accidentally do it yourselfyou can use Ctrl+F11 to lock the fields. Shift+Ctrl+F11 unlocks them when you're ready to make a change. Locking the fields won't necessarily stop miscreants from snagging credit for your work, but it can slow them down. Besides, you want to be in control of the fields you pop into a document. You don't want changes creeping in unmonitored.
Setting fields to work in your templates may not be as easy as humming a tune, but they can provide dynamic data updates when you have better things to do. And using them can add another whole section of instruments to your document composition.