I could regurgitate what I have read in the past about this, but it is done far better by Father Edward McNamara, professor of liturgy at the Regina Apostolorum university.
Father Edward McNamara wrote:
Q: Should the congregation follow the liturgy, including the readings, by using a missal? Some bishops and priests have said that the Word of the Lord is meant to be listened to, not read. Is the missal just for the other parts of the Mass? -- M.R., Greenville, Rhode Island
A: Although this is a point that is open to debate, it is true that the general preference is to discourage the use of reading as an aid to participation.
In 1998 the liturgy committee of the U.S. bishops' conference issued an excellent set of "Guidelines for the Publication of Participation Aids." With respect to the Liturgy of the Word, it said:
"By means of the word of God proclaimed at Mass, the Holy Spirit 'makes what we hear outwardly have its effect inwardly' (GILFM [The General Introduction to the Lectionary for Mass] 8). This, however, can only take place when the readings are proclaimed in 'a speaking style on the part of the readers that is audible, clear, and intelligent' (GILFM 14) and when sufficient amplification is provided (GILFM 34).
"It is clearly preferable that the word of God be clearly heard by all who participate in the liturgy, for 'In the hearing of God's word the Church is built up and grows' (GILFM 7). For this reason, the printing of readings and presidential prayers in participation aids is discouraged, unless other circumstances make it impossible for the word to be effectively proclaimed. Even in these instances, however, it is preferable that steps be taken to assure the effective proclamation of the Scriptures rather than resorting to providing a 'read along' text to the members of the assembly."
Therefore, the ideal is to participate by an attentive external and inner listening to the proclamation of God's Word and to the presidential prayers at Mass, rather than simply reading along with them.
He goes on to discuss some of the excellent uses of hand missals and the advantages of their use even in Mass. He concludes:
There is also a subjective element involved. Not a few people find difficulty in achieving the ideal of attentive external and inner listening for many justifiable reasons. I would say that if a Catholic finds spiritual profit in using the hand missal during Mass, then he or she is free to do so.
The very fact that the U.S. bishops' liturgy committee felt the need for these guidelines is proof that they had no desire to merely abolish the use of missals and other participation aids.
I strongly encourage people to read the whole link. In addition, I encourage people to read an additional follow-up that Father McNamara wrote, which with "Follow-up: Use of a Hand Missal at Mass [11-8-2011] Several readers wrote in asking for clarifications on the Oct. 25 piece regarding the use of hand missals."
at this link: http://www.ewtn.com/library/liturgy/zlitur382.htm
I also strongly encourage people to receive this instruction from the successors of the Apostles prayerfully, with docility and not put it aside merely because it disagrees with our preferences and it's not an authoritative instruction for the universal church promulgated from the Vatican. If we choose to disagree with our shepherds' recommendations, we should have good reason to do so.