Versatile hop.
I have found bittering from Cascade unpleasant, and yet one excellent and successful US lager, Riverwest Stein beer, uses it as a bittering hop at -2 hours. Who knows what they do right and I do wrong?
Agree with the above dry hop recommendation. As a dry hop it brings a lovely floral aroma it's hard to get any other way, but don't leave it in more than two days unless you like grass.
I'd dispute the above substitutions.
Agree it's one of the best hops to use alone for flavour and aroma, for the combination of floral and fruit, but in US Cascade the fruit contribution is distinctive but not overwhelming; the grapefruit character seems to vary a lot. Some AIPA brewers trash Cascade in favour of thermonuclear hops like Citra.
It combines well with many other hops. I've liked it with, variously, Galaxy, Simcoe, Nelson, Amarillo and Waimea, but in combination with any of those hops Cascade is always at least 2/3 of any late additions, so it doesn't get lost. Somewhere I saw an interview with the first commercial grower of Cascade, and she said their first buyers were mostly British breweries, before Sierra Nevada made it an American icon. I haven't tried it with popular British hops, Styrian Goldings, Saaz or other fairly subtle hops.