The traditional sequence is: build the wall solid, plaster it, then cut channels for conduit and back boxes, fill the channels, and patch the decoration. Each step damages the work before it. The channel removes the outer skin where the wall is thinnest; the fill is a different material with different movement; the patch is visible in raking light. On an acoustic wall the channel is worse than cosmetic — it is a direct path through the mass.
A cavity wall reverses the sequence. The frame goes up, the services run inside the cavity on pre-punched holes, and the boards close over them. Nothing is cut after the finish. The service layer is separated from the structural and acoustic layers by design, which is what the term service separation means.
The consequences for the building's life are larger than the installation saving. A wall with services in a cavity can be rewired or re-piped without demolition: on the clip-in system, boards come off and go back. A wall with chased services is effectively sealed — the next change means a new wall.
There is a cost argument, and it usually goes the wrong way. A cavity wall costs more per square metre than blockwork plus plaster, but the comparison stops at the wall. Add the chasing, filling, patching and repainting, add the facilities shutdown when the electrician needs to open a finished wall, and add the second wall that gets built when the layout changes — the cavity wall is cheaper over the life of the building.