[trouts2]

The boiler is made by Dunkirk.
One pipe steam with radiators.

A plumber said that using the big valve at the base of a radiator was bad way to turn radiators on and off as it messed up the steam system by taking away segment of the steam.

Could someone please tell me if that is correct and why?

I’m confused about it because of the following. I have found that there are temperature controlled valves that can be used in place of the usual turn on turn off by hand valves.
Many manufacturers make this style of radiator shutoff valve with a temperature control. They would be making and selling them if they were bad for the system.
What is so different about shutting a radiator off by hand versus having a temperature control shutoff the valve? Both are shutting off and turning on the valve.