The Good... All of the Operating System and Device manufacturers do push out mostly legitimate Software Updates. Usually these are designed to address bugs with fixes and to eliminate vulnerabilities. Often, new features are introduced. These are generally a good idea to do but never immediately. From personal experience, I have always found it a good practice to Google search and see the results of others first. Even with the best of intentions, with millions of applications out there, it is impossible to immediately test compatibility for all. If Apple releases iOS 12 and you see dozens of people who lost all of their contacts after downloading it, you wait for Apple to "fix the fix".
The Bad... Fake Malware (Scareware) is made to frighten people into buying protection. Typically, you'll get hit one of three ways. A Browser popup warning which will not go away until you clear the browser's cache is the most common. I received one of those yesterday on my Android's Chrome browser. It warned me that my device was infected with a virus and to click OK and then open a link. That is the worst thing you can do. Close the page and clear your cache. The second technique uses website advertisements. Typically, you click on a site that offers a FREE Web scan. It then finds "bugs" and recommends you various downloads to fix them. The most devious technique though is hackers making it look like the messages are coming from your message system or current Applications. In any of these cases, at best, you end up buying software you didn't need. At worst, you do get a virus or malware included in the download.
The Ugly... The proverbial wolf in sheeps clothing. These Software updates are sent out by the manufacturer and are legitimate in that respect. What's ugly though is when everything in these updates is not disclosed. Most recently, Apple released an iOS 10 patch that among other things, slowed down the processors of their SE, 6 series and 7 series iPhone models. This was done covertly and when busted, Apple claimed it was to preserve battery life or prevent freezes. Many of my fellow analyst believe the public is not buying iPhones as fast as Apple would like. What do you think the normal consumer does when they notice their phone is much slower and the battery capacity is diminishing? It may be no coincidence that Apple and the Carriers cannot give away the iPhone 8 series.
Oh, and Apple makes changing the battery as fun and easy as getting route canal dental work. Years ago, I recall having an older T-Mobile application that offered FREE long distance calling to Mexico which I loved. After blindly doing a software upgrade that the TM application pushed to me, I began getting an error message when trying to make my FREE Mexico international calls. It turns out that everyone that did the upgrade also lost this feature. Had I known, I would never have done this software upgrade. This is when I started Googling problems before installing anything. These are rare compared to The Bad and The Ugly problems but they do happen.
The motto of my story is, "If it Ain't Broken, Don't Fix it"! Unless the software upgrade specifically addresses a bug or an issue you are having, don't do it. For example... If the patch fixes a problem with APPLE PAY and you never even use Apple Pay, don't waste your time doing the software upgrade.