Combining and Integrating multiple single components, functional blocks and various technologies together to achieve required function, reduced size, mass, frequency response or other special requirements / functions usually results in complex systems / sub-systems.
Sometimes combining of dozen of standalone components to achieve required functioning would not be cost effective solution and will have envelope, size and mechanical construction that is not practical at all.
The right solution is integrated solution that also removes lots of unnecessary interfacing elements (e.g. connectors), merges some functional elements together and improve performances
E.g.: Front-End blocks, Complex Filters / Diplexers/ Multiplexers subsystems, Complex Antenna arrays alone or integrated with Front Ends or other Rf/Mw components, combiners for high power SSPA etc.
–See also STANDALONE COMPONENTS