Ok, not to give a flippant answer....
To make a distinction between 'updates' and 'upgrades', updates being the list of packages currently available in the repositories to add to a system or upgrade what is currently installed. Unless you are specifically referring to the list of available packages, I'm sloppy and use both terms mostly interchangeably. The Ubuntu Update Manager is an 'automatic' system *component* upgrade application. The distinction made there is upgrade vs dist-upgrade to fit in with their release strategy.
No. Updates are generally not necessary.
Sure you could update your list, but if you are not adding a new application, or updating/upgrading the current system, why bother?
The First Rule Of Most Anything is: If it's working; don't touch it.
The Second Rule Of Most Anything is: If you touch it and break it; you fix it or pay for it.
Contrary to most our training the questions that need to be asked are:
Is it working?
Will the modifications improve the system?
Will the modification break anything or impact another aspect of the system?
Take, for example by analogy, you have a car. There's 'nothing wrong with it', but, oh, a new model just came out.
You pick up the new model and it doesn't fit the garage...or less dramatic, the placement of some things in the garage need to be re-arranged...or two months later when you change oil you notice the catch pan does fit under the frame. The folks who put together your upgrade vehicle don't also make buckets that slide under them...and so the story goes.
As a 'real life' example,
Tor, the onion router found a teeny-tiny security hole that in certain situations could allow some malevolent force, or the NSA, to uncover the IP address of your machine. Unless your shipping missile launch codes...who cares?
The upgrade meant the handy plugin to easily toggle Tor on/off on the web browser no longer worked. Actually, it was just easier to have a dedicated web browser for Tor. So, because of a fix that didn't affect 99.9999% of Navigatrix users you have a mess.
Having said that, I upgrade frequently, most of the time it is for no good reason what so ever.
Most of the time it is a change that doesn't affect me; security threats, the NSA, teenage zombie bots; and I don't even notice.
Occasionally, there are cosmetic or function changes that do catch my eye. Some are better....some not. Occasionally it just means I have to reconfigure something I reconfigured the last time I upgraded...or learn a new way to do something.
For example, sometimes websites will have a javascript that prevent the selection of text to copy and paste it to another application. The updated Firefox removed the 'javascript toggle' to allow you to block javascripts if you want.
Now, with an upgraded Firefox, if you want to copy'n'paste from those websites you either need to install an extension, or crawl into the Firefox configuration file.
The frequency of updating is also burdensome. There are over 100,000 files that get updated with differing frequencies. There are more than 5 patches per hour in the kernel. Major release time has shorten from months to weeks. Most of the changes don't affect us mere mortals as there are two rules to most anything....
