GIRM 368-370: Various Needs and Occasions 1

When a special need arises, the Mass can be utilized for prayer:

368. Since the liturgy of the Sacraments and Sacramentals has as its effect that for the faithful who are properly disposed almost every event in life is sanctified by the divine grace that flows from the Paschal Mystery,[Sacrosanctum Concilium 61] and because the Eucharist is the Sacrament of Sacraments, the Missal provides examples of Mass formularies and orations that may be used in the various occasions of Christian life for the needs of the whole world or for the needs of the Church, whether universal or local.

369. In view of the rather broad possibilities of choice among the readings and orations, it is desirable that Masses for Various Needs and Occasions be used in moderation, that is, when truly required.

370. In all the Masses for Various Needs and Occasions, unless expressly indicated otherwise, it is permissible to use the weekday readings and also the chants between them, if they are suited to the celebration.

Moderate use: what would that look like? Once or twice a year, I would think. There are probably priests and parishes that never utilize them.