I see the Liturgy Committee as being part of the planning process for Mass. The need of importance of this planning is discussed in the GIRM.
From the 2002 General Introduction to the Roman Missal (GIRM) which can be accessed from
romanrite.com/girm.html :
“106. It is appropriate, at least in cathedrals and in larger churches, to have some competent minister, that is to say a master of ceremonies, to oversee the proper planning of sacred actions and their being carried out by the sacred ministers and the lay faithful with decorum, order, and devotion.”
“111. Among all who are involved with regard to the rites, pastoral aspects, and music there should be harmony and diligence in the effective preparation of each liturgical celebration in accord with the Missal and other liturgical books. This should take place under the direction of the rector of the church and after the consultation with the faithful about things that directly pertain to them. The priest who presides at the celebration, however, always retains the right of arranging those things that are his own responsibility. [footnote 90: Cf. Second Vatican Ecumenical Council, Constitution on the Sacred Liturgy, Sacrosanctum Concilium, no. 22.]”
“352. … Since, indeed, a variety of options is provided for the different parts of the Mass, it is necessary for the deacon, the lectors, the psalmist, the cantor, the commentator, and the choir to be completely sure before the celebration which text for which each is responsible is to be used and that nothing be improvised. Harmonious planning and carrying out of the rites will great assistance in disposing the faithful to participate in the Eucharist.”
There is a better translation of this last sentence of n. 352 in the GIRM of England and Wales: “Harmonious planning and carrying out of the rites will, to a great extent, help
dispose the hearts and minds of the faithful to participate in the Eucharist.”