I like having an electronic indicator of the vacuum. Set up the camera the night before, and a quick turn on to see the vacuum is still in place in the am. Also before each dive on the boat lets me know all is still well.
One caveat with the Leak Sentinel system (Vivid Housings). When you turn the unit on, it senses the pressure in the housing as atmospheric pressure (1 bar) and measures vacuum relative to that pressure. So if you pull a vacuum at night and then turn the sensor off afterward, when you turn it on in the morning, it will sense the internal pressure (approx. 0.8 bar) in the housing and measure vacuum relative to that pressure. So, although you may have a vacuum in the housing, the sensor will indicate that there is not a sufficient vacuum in the housing and will blink red.
Although I have not dove the unit yet, I plan to pull the vacuum at night after the unit is assembled for the next day and monitor it for 30-60 minutes. If all is well, I'll turn the unit off to conserve battery, but retain the vacuum in the housing. The next morning, I'll bleed air into the housing to eliminate the vacuum as evidenced by the hissing sound. If there is no hissing, then I have a problem. Then reestablish the vacuum with the proper green light indication. Using this procedure, I should get a 14 day dive trip out of one battery, or at least I hope to do so.
I cannot comment on how other systems work.