Both silence and vocalization have their own merit.
Reading aloud does not give me as big a sense of freedom as reading silently does, since I find that reading silently provides me with more opportunities than reading aloud does. When reading aloud, I find myself unable to thoroughly process what I have been reading, whereas when I read to myself, I find it simpler to ingest the information which is presenting itself to me on the page before me. Furthermore, as an active introvert, I find it easier to understand content on my own rather than going through text vocally (in a way which reminds me of presenting ideas to other people).
Reading something exclusively for myself within the confines of my mind allows me to focus on every word tying itself to a passage, invites me to create a personal mental image that nobody has ever seen but me in the book, whereas reading the same passage aloud, be it to myself or to others in my vicinity, I cannot quite as easily envision the contents of a passage — my voice-to-brain filter is not as well-formulated as my brain-to-brain filter, and it takes longer for me to process information and pair it with a mental image than it does for me to simply translate a written text into my mind and conjure up a personal understanding of it. Though I would love to share this mental image of mine with others, translating words into an image and then back into words will only confuse the audience to which I am reaching out, thereby rending it thus: I can either read aloud to myself or others to look for a way to evaluate a text as a group, to find a deeper meaning in it based on facts and shared images, or I can read a text to myself and grasp the information it is presenting to me with the help of my personal sensory memories and other cognitive triggers.
On a side note, I write by configuring words in my mind and transferring them onto the page as my mind comes up with the proper words, and so do I read. Reading aloud triggers memories of reading aloud in class in my head, and I feel as if I am restrained by a time limit, that I cannot go back and fix the mistakes I made whilst reading or figure out what exactly the text was talking about which I completely missed whilst trying to effectively render written words into speech. Reading in my head helps me UNDERSTAND what I am reading — it allows me to stop, take a moment to digest the words, to loop them together and supply them with a mental image. Reading aloud constricts me with memories of rushing through a script in class. However, I must sometimes read a passage aloud, slowly articulating each sound, every word, in order to gain access to my concentration and to allow myself to only think about the text before me. Much like St. Augustine mentioned in his Confessions, I find that every person who chooses to read to him/herself rather than reading aloud has a reason to do so, and that this reason is beneficial to the person in question.
Borges, Jorge Luis. “On the Cult of Books.” 1951.