The problem with the cancel option in run now for scripts is the cancel button runs the script, just without any saved changes. This is not what cancel means.

Open a script:
Change target machine

Click Run Now.

You receive a pop up window that says: "There are unsaved changes to this
page; OK to Save before running, Cancel to Run Now without saving."

This can lead to a huge headache, for example.

There are three computers, A, B and C.

Last time I ran the script, I targeted machine A.

Now I want to target machine C, however I accidentally selected machine B,
and click Run Now.

I now have two options: target machine A, or target machine B. I cannot
cancel and change to the intended target, machine C.

The options should be OK to save and run, Cancel to review changes.