It depends form many factors, simplest way to think about this is finding the most relevant landing page.
e.g.
red prom dress, cheap red prom dress, prom dresses red
all are one group, while
blue prom dress, blue prom dresses , cheap blue prom dresses
would create a different group and would link to page, e.g. blue-prom-dresses.html
while the first group would link to: red-prom-dresses.html
Makes sense now?
E.g. pluss size red dresses probably would make another campaign going to plus-size-red-prom-dresses.html
