Updates do three different jobs that often get confused: they fix security holes, they repair bugs, and they change how things look and work. The first two are close to mandatory; the third is what makes people avoid updating at all.
Security fixes matter because the details of a flaw become public when the patch is released. Attack tools follow within days, targeting exactly the people who postponed. Delaying a browser or operating system update for months is the single most common way ordinary devices get compromised.
That said, timing is reasonable. Installing a large update ten minutes before a presentation is asking for trouble; installing it on a Friday evening with the charger plugged in is not.
Failed updates are usually mundane: not enough free storage, a battery too low to proceed, or an unstable connection halfway through the download.