Are windows updates necessary?

Avast has been protecting my xp and win7 for many years. Never had a virus. I just did the offline sp1 and 2016 roll up etc and still have to decide which others to install, maybe. System runs fine just a little slower on startup.
But the time and downloads, is it necessary? I currently keep two separate images of system and data partitions, easy to re-image if I ever need it.
I have limited bandwidth usage/costs and not sure of the benefits of windows updates.
So I’m asking, thanks, Moe

Yes they are needed.
They contain fixes for the OS including security leak patches.

Ordinarily OS updates are most certainly required, the problem being XP is off official update support. So it may be more vulnerable because it is no longer supported (but avast continue to support it) and may be more vulnerable to attack/vulnerabilities.

XP still has a relatively large market share, still more than windows 10 and as such could still be a worthwhile target for malware.

So you need to be more proactive in your approach to security and having backups is just one method. In XP I run DropMyRights on every internet facing program (browser/s, email, etc.), whilst this doesn’t prevent your getting infected, but it can limit the damage.

As you can see from my signature (below my posts) that I still use XP as my main system even though I also have win7 and a very recent notebook purchase with windows 10. On this XP system I do a weekly full system backup (Drive Image) and I keep the last six backup copies.

There is an unofficial way to continue to receive udates for Windows XP
You learn more about it here:
https://forum.avast.com/index.php?topic=176600.msg1253353#msg1253353

Sorry I don’t mean to start an oil thread I’m just asking if avast and mbam find the problems as quick as MS? Or is it not similar? As for Update patches why bother.
Data usage is the biggest reason I will stay with 7. I do keep 1 original image set up the way I like. And I make a new image each month.
I know avast has warned me when I web browse that a site is dangerous.

avast nor MBam solve security leaks in a OS.