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The Luxury Collection, Autograph Collection, and Tribute Portfolio are "collection" brands (with The Luxury Collection being the highest tier). These brands are secondary to a hotel or resort property's own name, personality, and reputation. The quality standards are high, and the locations are usually excellent.

Delta and Four Points are conversion brands. The former is for full-service properties and the latter for select service properties. Let's suppose you're the owner of a Ramada Plaza or Ramada Inn at an interstate highway offramp. You want a boost from Marriott's marketing and loyalty base. You're willing to invest some money, but not enough to meet the standards of a "real" Marriott Hotel or Westin Hotel. Maybe your location isn't what guests of those brands expect either. Replace the flooring and furniture, but keep the old HVAC and bathroom fixtures. Convert to Delta or Four Points.

Project Mid-T will result in a conversion brand in the “Midscale” tier. The actual name of the brand has not been announced. “Midscale” is below the tier of Fairfield Inn, Moxy, and TownePlace Suites.

The lodging industry has six tiers: Luxury, Upper Upscale, Upscale, Upper Midscale, Midscale, and Economy. See https://www.hotelappraisers.com/hotel-brands/ for how brands map to these tiers. Fairfield Inn, Moxy, and TownePlace Suites are "Upper Midscale."

With this new conversion brand, Marriott should be able to attract all sorts of limited service hotels from the lower-end brands of Wyndham, Choice Hotels, and smaller companies. Also, Marriott will be able to rebrand older, smaller Fairfield Inns that are below current standards, instead of watching those properties leave.

It's probably a good business move for Marriott. But what a complicated brand structure!