All Hawan which are performed with some desire (i.e. Kamana) should be performed when Agni resides on Prithvi i.e. on the Earth only.
However, for other activities which are routine, Agnivasa is not considered e.g. Chandi Homa during Navaratri, routine Homa performed by Agnihotra, Homa during eclipse, on Amavasya, on fasting day, activities related to Sanskara like tonsure, thread ceremony, marriage, travel etc.
Agnivasa depends on the combination of Tithi and Weekday. Agni might reside at one of the three places -