the pattern says to use interfacing...do i really have to,or its just a little extra?thats the dress http://compare.ebay.co.uk/like/261264454048?var=lv<yp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y&cbt=y&lpid=63&device=c&adtype=pla&crdt=0&ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=63&ff19=0