Each tradition has 5 they spirits that practionners can summon. I understood that, but, aside from roleplaying, why are they classified by domain? A shaman has 'Beasts' in Combat for instance.
The only thing I found that was dependent of the type of spirit is the 'Sustain spell' service where the awakened has to use a given (by his tradition) spirit. Is it the only use?

p. 178

Magical Services: Th e magical services available from a
bound spirit are Aid Sorcery, Aid Study, Spell Sustaining, and
Spell Binding. A spirit intended to assist the magician with
magic must match the category of magic, according to the
magician’s tradition.