Used to be, not long ago, a priest visiting a parish, any parish, could fully expect to say mass, either concelebrated or otherwise, in agreement with his priestly responsibility to offer the holy sacrifice once a day and in a sacred place, for his own good and the good of the Church.
The Church wills that priests normally say mass ever day, in church, with faithful present.
(Cf. Canon 904 strongly recommends the priest celebrate every day; Canon 902 gives the priest the right to celebrate the Eucharist individually except at the same time of a concelebration in the same church; Canon 932.1 makes it normative that mass be said in a sacred place, except when in a particular case it is necessary to say it in some other decent place; Canon 903 requires the host church not to forbid it, when it can be prudently judged the priest is in good standing; and Canon 906 normatively prohibits saying mass alone, except for a just and reasonable cause.)
These canons taken together are to be interpreted liberally. The attitude is let the priests say mass, for their own good and the good of the church, and let people go to those masses. The more the merrier.
In recent years it has become normative throughout the United States for churches to refuse visiting priests this age old privilege of saying mass in church, even when it is certain that the priest is in good standing, often in the name of "Protecting God's Children." This new restriction can have only two effects: either the priest will not say mass that day, to the detriment of the Church and to the world, which would otherwise benefit from the spiritual good of that mass, or he will celebrate the mass in a place which is not sacred. The latter is harmful to church unity.
What is more, the visiting priest may hear confessions at the parish, shrine, etc. without anyone's permission, while he is refused to say mass!
This new norm of priests routinely refusing priests the right to exercise their priestly duty is contrary to justice, it contradicts the standing law of the Church and an age old custom, and violates basic Christian charity.
The "celebret" has literally become a dead letter! Shame!
"And hospitality do not forget; for by this some, being not aware of it, have entertained angels." Hebrews 13:2