When we first moved into our 1790’s home, I bumped my head many times on a sloping ceiling in the master bath. I could not wait to change that situation. One of our first major additions/renovations included a full height master bath. We still have a sloped ceiling in the new bath, but it starts at about 7’-0” and goes up from there.
Ideally the sloped ceiling starts high enough so that furniture easily fits against the walls of the room. If you end up with low ‘knee walls’ you can fill in along the edges with bookcases, shelving, or storage space. There are many great ways to utilize the space in the low spots.
Though I don’t like to bump my head, I do love to see the structure expressed in a room, whether by exposing beams on a first floor or by expressing the shape of the roof in the ceiling by insulating between the rafters. One of the most interesting characteristics of the resultant complex ceiling lines is the way reflected sunlight changes its appearance throughout the day.