Vaishvadevam is a mandatory duty of a married man (grihastha). There 5 places where a grihastha can acquire sins due inadvertent killing of other living beings. Vaishvadevam must compulsorily be performed to atone for such sins.
Vaishvadevam must performed after learning from a preceptor and must be performed only by married men and not others. It is performed both during day and night times following the prescribed procedures and by invoking all Devatas.
Partaking food is not only to satisfy a hunger. Many precepts need to be followed. It is called Anuyagam and is performed after Ijjya Aradhanam. Swami Desikan has shown that it is a yagam (sacrificial offering) for the sould (Jivan) that is atomic in nature.
To know what the 5 types of sins are, the procedures for performing this, the time when it should be performed and to learn why eating is called Anuyagam and its significance and procedure for doing Anuygam, refer the link below.
https://youtu.be/qkTkX2R276s – Sri Desikan Anushtanam – Vaisvadevam & Bhojanam | Vande Vedanta Desikam