Beam on side of CRT

I was reading some of Tim Skelly's history, and in it there was a brief
discussion of a watchdog circuit (on a vector game) that reset the machine
as necessary. The purpose of this was to avoid the possibility of shooting
the electron beam into the side of the CRT in a game failure condition.
There was no discussion of why this is bad...

Anyone want to offer logical explanations or actual experiences with
shooting the beam into the side of the CRT?

Other than curiosity, I have some interest because my AD displays slightly
wider than the screen. I'm not aware of any width adjustment on the
deflection amp -- are the X & Y gain on the main PCB used for H/V width
adjustment?

Thanks

---
Bret Pehrson
mailto:bret@infowest.com
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