If your main isolator switch was causing a drop of 1v then yes it will make a big difference. Ocasionally operate the switch as this will help keep the contacts clean.
I think you are being told rubbish about your inverter ...microswitch ??? total load of bullshit....If your inverter is working /powering your loads fine ,not over heating or blowing its fusing then its fine.The only place power can disapear to is heat ..... Bet the person who told you this sells them .
I suggest you dump the person who is your electrical advisor