I like aluminum pipe wrenches because of their light weight.  I have a whole collection of Rigid aluminum wrenches for various applications.  The job is always easier with the right tools.  I use this one for working in  sink cabinets where space is tight, but I still need the leverage a  10" handle provides.  I suppose there is not a great deal of weight  difference between this wrench and a cast iron one, but the aluminum will  never rust.  This is more a problem if you are working around corrosives  like liquid fertilizer, but old habits (buying aluminum) die hard, so it  was a natural for me to buy this wrench.