Ooooh. If your pool guys is useless for equipment and answering that question, he's probably not so good in the chemical department either.

Unless I'm missing something, the top valves you show above simply divert water to different areas like your pool returns, spa, etc. The second pic adjusts the "pull" of water from those locations - back to the pump. There should be no reason to lose water from adjusting those valves - unless there is a leak from one of those areas. And since you have a cartridge filter, you don't do backwashes, so there's no water loss there either.
If you suspect you have a water loss, you might want to checkout this page:
Pool School - Leak Detection.
Please let us know if you have any more questions.