Nanoplasmonics represents one of the most extensive research fields in optics on the nanoscale and has emerging applications in sensors, light-emitting devices, and photovoltaic devices. It offers a number of effects and can be combined with existing technologies by a number of approaches, the colloidal techniques representing the easiest implementation in the existing and emerging photonic components and devices. In this article, plasmonic effects are discussed in terms of three major physical phenomena (incident field enhancement, photon density of states enhancement, and nonradiative decay enhancement) in the context of various photonic processes and devices related to Raman scattering, photo- and electroluminescence, photovoltaics, photochemistry, and photodetectors. A number of instructive examples are given for metal nanospheres and nanorods showing how size, shape, core-shell design, and ambient environment can be used to get maximal use of the favorable factors while keeping unfavorable ones at reasonably safe level. A number of aspects of plasmonically enhanced secondary radiation are emphasized which have not gained close consideration to date. Among them, the following properties are discussed: the decisive role of scattering component of metal–dielectric extinction spectrum overlapping with incident and emitted/scattered light wavelength, valuable contribution to enhancement factors from spacers used to prevent emission quenching but simultaneously affecting the extinction spectrum, a pronounced dependence of enhancement factors on dielectric permittivity of the substrate, dielectric shell, and ambient medium.