Fitted bathroom furniture is usually defined as a series of bathroom furniture cabinets in a row like for example in a kitchen, mostly fitted with a plinth at the base which helps to conceal unsightly pipework. These products can also be purchased as either floor stand standing or wall mounted.
Modular bathroom on the other hand has its furniture usually defined as a singular or a multiple run of matching but individual bathroom furniture. These products can be purchased as either floor stand standing or wall mounted.
Other considerations, wall hanging bathroom furniture tends to make the bathroom look larger and leaves the floor is easier to keep clean. It also helps in preventing damage to the bathroom furniture should the floor get wet. Probably best to consult your professional installer/plumber for advice.