The majority of new homes constructed are built on a slab. To do a traditional nail down installation the floor needs to be specked out during the design phase to accommodate a subfloor otherwise elevations will be affected causing the need for transitions that can take away from the smooth flow from room to room. Glueing a solid or engineered floor directly to the slab can be one way to reduce or remove the need for chunky reducers and offer a more elegant flow from to room to room. Advantages of glue down applications is that the floor elevation is not raised and a solid feel and sound as opposed to a floating floor installation that can at times give a hollow sound especially if a quality underlayment is not used. Disadvantages to glue down installation can be the additional cost and time to do a glue down installation. Also removal in the future can be a huge task as the glue that is used these days is extremely strong and difficult to remove. Sometimes the wood boards are removed in the smallest of slivers from scraping and chizeling of the floor. The options for glue are much better now and things to consider are whether the glue has a moisture barrier component, whether it has a memory quality and ease in cleanup. Another consideration is whether the slab has radiant heating. Radiant heat can cause extreme ranges of heat in a single room. Some engineered floors are rated for radiant heat while others are not compatible with radiant heat. Check with the manufacturer to determine if the engineered floor is suitable for the application.