I don't full time (which means giving up your house), but on long part-time journeys I've met many people living full time in TTs (and even pop-up campers).
These have ranged from singles and couples in 13 foot and 16-18 foot egg trailers, couples in 24-32 footers, families with 4-6 children in 28 foot TTs. Some were retired and doing this as a lifestyle choice, most I've met were doing it because they were moving around from job to job in businesses where projects are finite, jobs are temporary and hundreds of miles apart. Which probably says something about the kinds of places I choose to stay when moving around in my RV.
Different people need different amounts of space. When it comes to full timing, you may be carrying your whole life's baggage with you. You need room for that too, however much it is. I've had people working for me who could put their life (one including his Triumph Bonneville) into their VW Type 2, know others that needed three forty-foot containers to move two peoples indispensable stuff between jobs in the U.S. and overseas.
A 24 to 30 foot TT and a tow vehicle with some extra cargo capacity fits someplace between those two extremes. A 45-foot motorcoach pulling a 20 foot cargo trailer fits in another place in between. You either adjust your lifestyle to the space, or adjust your space to the lifestyle.
As for me, I am encumbered by the goods left behind by the women in my life, not mine to throw away, taking up space I would not otherwise need.