Do you sit down at your users desks when they have a problem and then login as a Developer with Full Access so you can fix the bug?
If so, you've given up any security you might have set up on your own computer. And the user can watch what you type as a password.
Other things to consider is that the user may have installed a key logger or while talking on their cellphone use its camera to take a movie of your keystrokes...
Before 14 I used Roboform to capture you account name and password and I set it to enter those for me in FileMaker's dialog. 14 seems to have killed this or else I can't remember how to set it up. But there are other password managers that might do this.
14 has that little checkbox for remembering the password for Full Access users. If your account name is John Smith and that checkbox becomes checked when you log in at the user's computer (is that posible?) then they only have to open the file and it will open with your account name. Of course, no developer would do that, right?
And, of course, don't forget to logout before you leave the user's workstation... If you leave the Full Access acount open then anyone can sit at that desk and do anything they want including creating their own full access acount or changing your password, etc.
In other words, sitting at someone else's desk, logging in with your full access account to debug or add something while convenient is not a good idea no matter how many times we have all done this.