What pump are you running (brand/model) ?

The vacuum gauge will tell you many things...like how much vacuum you have when all zones are open and nothing is on top of the bleeder/spoilboard...how much you have with a sheet of plywood or MDF on top and all zones open...starting vacuum, vacuum as you cut through & vacuum at the end of the job with all that open kerf. This is information you NEED to know in order to determine usable vacuum (how much you have with something on top - how much you have with nothing on top = usable vacuum. This will vary depending on bleeder material.)

Every job is different & in some cases requires a bit more than turning the vacuum on...as in - carefully thinking out the toolpath layout on jobs with a lot of open kerf to turn off zones that are done to save vacuum...or as Jim mentions, onion-skinning - or cutting 90% through everything then coming back and leisurely cutting through that last 10% to minimize part movement and maximize the usefulness of the vacuum.