Excellent

Example: Microsoft Visual Studio. You finish your work, and when you exit from Visual Studio, it prompts you with “Updates are available, would you like to install them now?”. There are Yes and Cancel (= defer to next time) options.

Good

Examples: Idea IntelliJ, Topaz Photo. While you are working the program checks for updates in the background. If they are available it shows a subtle notification which does not get in the way of your work. When convenient, you click on the notification to start the installation process.

Also Good

Example: Windows Update. A background process detects available upgrades which are silently installed while you work. If they can be completed without interrupting usage, that’s done. If not they are deferred until either you choose to reboot the machine, or it can be done automatically when not in use.

Acceptable, Most of the Time

Example: Microsoft Office 365. A background process detects available upgrades, which are silently installed while you work. Occasionally there’s an annoying notification that Office needs to be closed down for a short period to complete installation, but you have the option to defer.

Wholly Unacceptable

Examples: most meeting and messaging apps. You go into the software just before your meeting. It looks for updates and if they are available starts to install them. There is no option to defer.

Why, just why?