From my short experience and limited research, you don't have to. Most DME and LME have already been boiled and don't even have to be boiled. The boiling is for the hops and allowing the bitterness to become soluble in water. You should look into late extract addition method (which I have about 2 days ago) and found it can save you $ on hops, add more flavor, prevent the extract 'tangy-ness', reduce needed boiling time, improve 'crispness', and allow for light color. This is what i think...I just did my first late addition extract (IPA) tonight so if all turns out as planned, it should be better than most extract brews and saved me $ on hops.