They often are an elite unit of the regular armed forces, or are designated as such, and may maintain special rights or privileges.
Royal guards have historically comprised both purely ceremonial units serving in close proximity to the monarch, as well as regiments from all arms, forming a designated substantial elite and intended for active service as part of the army.
An example of the first category would include the Tropas de la Casa Real of the Spanish monarchy prior to 1930, comprising halberderos and a mounted escort.
The modern Garderegiment Grenadiers en Jagers regiment of the Netherlands and the Escorte Royale of Belgium retain features of uniform and other distinctions that can be traced back to Napoleonic influences.
In times of revolution, the continued loyalty or defection of such units has often played a key part in the outcome of wider unrest.