Laying the substrate allows you to extend the life of the flooring — according to some sources, the life of the laminate increases by 2-3 times. In addition, the use of underlays makes the indoor environment more comfortable.
Laying the substrate allows you to solve several problems at once.
Laminate is usually called (and it really is) the loudest coating. It is very hard, so even if you just walk on it, the resulting sound will be loud enough, not to mention walking in heels. The situation is aggravated if the laminate is simply laid on the subfloor. An empty space is inevitably formed between the rigid lamella and the rigid base. This volume will act as a kind of acoustic amplifier, thanks to which the sound will spread both throughout the room and down to the neighbors.
An uneven base will significantly reduce the lifespan of the flooring, especially the laminate. Due to the depressions or protrusions, the lamellae warps, the pressure on the lock connection turns out to be unequal, the lamella itself begins to sag and level out, which over time will lead to a violation of the integrity of the lock fastening, the floor covering will begin to disintegrate. Laying the underlay allows you to smooth out relatively small (up to 2 mm) irregularities.
Wood is a hydrophobic material, it is able to absorb and accumulate moisture, while its linear dimensions increase. If a laminate or parquet is laid on a black concrete floor that is not sufficiently dried, then after a while the floor may swell — the moisture contained in the concrete will be absorbed by the floor covering, the lamellas will expand and begin to squeeze each other out. Especially the floor coverings on the lower floors need to be insulated from the effects of moisture; if the waterproofing is broken, moisture from the soil through microcapillaries inside the concrete mass can rise not only to the first, but even several floors up.
Concrete floors have a fairly high coefficient of thermal conductivity, very often they act as «cold bridges» through which heat loss occurs. Laying the substrate allows you to obtain a good thermal insulation layer, which improves the comfort in the room by reducing heat loss. At the same time, the temperature in the floor area also rises, so it is pleasant to walk on it even barefoot. But as in the case of soundproofing, don’t put too thick a layer of underlayment under floating floors — this can lead to breakage of the locking joints.