Hello Ekki,
there are interesting discussions on the reflector, for instance here:
According to the general rules, chapter 3.7.1 “Criteria for a valid Expedition”:
8. […] QSOs must comprise an exchange of callsigns and signal reports, it is strongly recommended that the summit identifier be given during each contact. […]
On the bands, the summit reference is usually announced less frequently. Personally speaking, I give my reference in the first QSO on each band, during S2S-QSOs, upon request and else every 3 or 4 QSOs.
If the pile-up is dense, which is often the case on 40m, I keep the QSOs rather short, like contest style.
73, Roman