It is largely a matter of convenience. If you are a tent camper you would have no problem with no toilet or other amenities.
If you are a minimalist then an separate holding tank might be fine but make sure the grey water does not dump on the ground or you may need two holding tanks.
If you like conveniences, theses day you are only limited by your pocket book.
We came from a canoe and tent background, so when we decided to travel and see the sights, we wanted; a bed we could exit without crawling over the spouse, a bathroom we could move around in, a pantry and closets so we would not have to pack and unpack our food and cloths and room enough for two adults and a dog on a rain day.
We are happy with a 25 ft. TT, which s still small enough to wind through city streets to fine a quilt shop.
Some would find ours to big, others would find it way to small. Only the buyer can say for sure what they want and need.