This problem was always a sticking point for Cops wearing body cams. They don't want their conversations and actions recorded the entire time they are on a call for fear it picks up something they didn't intend/want. So, if the cameras are able to be turned off and on, it's a given that we'd see "gaps" in the recordings where the Cops said they "forgot."
I don't think any of us would be comfortable wearing a recording device the entire time we are on the clock at work. Cops have an especially difficult time given the amount of public scrutiny even the most routine case receives once someone decides to make it go viral on social media.
Having said that, there must be a way to remote activate the cameras (if not now, with an upgrade?) so when a dispatcher assigns a unit/officer to a call, the cameras are turned on immediately, and they can't be turned off until the unit/officer changes status to something other than working that case.
It's not that we can't trust all the Cops to do things right. These cameras are supposed to catch Cops AND THE PUBLIC when they do things wrong -- so we, the people, can be sure we are getting all the facts in a case.