In 'Witches Abroad' they have to leave their comfortable(ish) homes in rural Lancre and travel abroad to sort out a fellow witch who has an urge to bring order to the city of Genua by imposing the predictability of fairy-tales on the unsuspecting populace - Emberella has to marry the prince, even though he's a spoilt, snivelling runt. Abroad is not a place that Granny Weatherwax approves of, but "Wisdom is one of the few things that looks bigger the further away it is." So they have to get close to see the detail, not just the mass, and find out what's actually going on.
The witches are amongst my favourite of Pratchett's creations. He enthusiastically wrote any number of great female characters into the Discworld, they were merely the first. He takes stereotypes, defys and builds on them to create full-blooded, comic characters. Needless to say the book is very funny and the dialogue between the witches is the basis of much of the humour.