Let’s take this scenario:
You made the last imagefile at the start of February.
Late February you installed a couple of new programs and in mid March you also tried out 2 new shareware programs.
They didn’t live up to your expectations; so you uninstalled them again.
All along you’ve surfed the internet and used the computer as usual.
The installation of the new programs was a bit tricky, but after a couple of retries and some assistance from a hotline you succeeded in installing the programs.
At the end of March the computer is still running smoothly.