Your own speed affects the ability to make some kinds of measurements. I believe I remember the bit you're talking about, very vaugely. Its dependent on the kind of measurements you're taking.
One thing to note is that if you are setting your TDC for instance to a particular range and you are driving towards a target then over time this will skew your solution as the range becomes more and more different from the one you entered. In this sense firing from a low speed or a stand still is better. However this is the opposite for instance if you're in between columns of a convoy where you're going at the same speed as your targets.
Own speed is just another variable you have to track. Most of the time all you have to do is compensate for it a bit more than if you were stationary. For some methods though, such as this Ujagd one, it is a bigger deal, but overall there is really no set speed to operate at since situations are unforseeably variable.
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