Suppressing EMI from mains and getting power in-series with a capacitor are just the two main function of these front line capacitors and is discussed in this app note from Vishay. Link here (PDF)
Because of the high energy availability and the severe environment of surge voltages and pulses, applications of capacitors in connection with the mains must be chosen carefully.
Two kinds of connections, and thus two kinds of applications, can be distinguished.
One is where the capacitor is directly connected in parallel with the mains without any other impedance or circuit protection, and another where the capacitor is connected to the mains in series with other circuitry.