Charging my in-ground sprinkler system

How important is it to "gently" charge my in ground sprinkler system in the spring? When the guy came over to blow it out last fall, I asked him how to charge it in the spring and was told to just open up the valves. So last night I did just that. I turned on one of the zones of my system, and then opened up all of the shutoff valves. All of the heads are working fine, so it appears that all is well. However, I was doing some reading today, and it seems that I was supposed to only open up the valve part way, to reduce the water pressure, as well as remove a sprinkler head from each zone in order to let the air out. How important is it to do this? Am I safe as long as all of my heads are working, or is there something else that may have broken? Does everyone else use the "just turn it on method" or do you all remove the heads and open the valves up part way until the system is charge?
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