Right skimmers are not essential but they do help in certain tanks.
Like donya said they strip the water of organics which is both good and bad, on one hand they remove waste and oily protiens that cause pollution but they also remove small food particles (phyto, rotifers etc)
To say you haven't done a W/C for 6 months is a bit misleading, do you dose your tank with anything? Calcium? Essentials? Because many of us use W/C as a primary means to replenish the mineral content of our water as well as using it as a nitrate remover.
Do you run calcium? Nitrate/phosphate reactor? What's your stocking? Do you have a sump? DSB? Dose a carbon source? Add minerals to top up water? Do you dance in front of your tank naked at a new moon doing the purer water jig?
Do you test your water on a regular basis? If so what are your stats? Anyone can say that something works/fails for them but without other information it's hard to advise or congratulate
) )
Tbh my water changes are down from weekly to fortnightly just because my stats are starting to even out (just started a few different corals off) however the other tank I have planned (which is 15g) will need to be skimmed heavily and will be subject to weekly 30% W/C but that's a different story.