Some routes with early difficulty where combining pitches is a bad idea: Classic, Son of EO, Maria Direct, Higher Stannard, Drunkards. Absurdland (OK, there's no real 2nd pitch here to combine), Three Vultures, Directissima, Double Crack.

Probably a few at Near Trapps, but I'm not gonna rack my brain to think of them. Broken Sling and Criss Cross do come to mind however.