Usually a Church always has the Blessed Sacrament present in the Tabernacle, otherwise every time Communion would be distributed, one would have to extinguish the sanctuary lamp.
Of course they do, but for the purposes of this thread, the priest might have that ciborium with him distributing Communion.
Moreover, regular, weekly Benediction after Mass (as occurs in many chapels) would not be possible unless the Holy Eucharist was always in the Tabernacle.
Also I've read that the priest consecrates a second host at Mass on the day of Benediction as they are not allowed to have a consecrated host kept for any length of time (that's why they distribute from the ciborium in the Tabernacle before the one they've just consecrated.)
So in a parish church the Blessed Sacrament will always be in the Tabernacle except when the priest is distributing Communion it
could be empty.
- The tabernacle may contain a pyx for Communion calls.
In the churches I've done sacristy work, pyxs are kept in the sacristy never in the tabernacle for the same reason as stated above for the lunette.