  Planck, SPT and ACT surveys have clearly demonstrated that Cosmic Microwave
Background (CMB) experiments, while optimised for cosmological measurements,
have made important contributions to the field of extragalactic astrophysics in
the last decade. Future CMB experiments have the potential to make even greater
contributions. One example is the detection of high-z galaxies with extreme
gravitational amplifications. The combination of flux boosting and of
stretching of the images has allowed the investigation of the structure of
galaxies at z ~3 with the astounding spatial resolution of about 60 pc. Another
example is the detection of proto-clusters of dusty galaxies at high z when
they may not yet possess the hot intergalactic medium allowing their detection
in X-rays or via the Sunyaev-Zeldovich effect. Next generation CMB experiments,
like PICO, CORE, CMB-Bharat from space and Simons Observatory and CMB-S4 from
the ground, will discover several thousands of strongly lensed galaxies out to
z~6 or more and of galaxy proto-clusters caught in the phase when their member
galaxies where forming the bulk of their {stars. They will also detect tens of
thousands of local dusty galaxies and thousands of radio sources at least up to
z~5. Moreover they will measure the polarized emission of thousands of radio
sources and of dusty galaxies at mm/sub-mm wavelengths.
