Sometimes we like a greeting card that’s blank on the inside so we can write our own thoughtful message-- and sometimes, we like a greeting card that has a preprinted poem that phrases things far more elegantly than we can string our thoughts together. Memorized/formulaic prayers are kind of like that-- where when our own words fail us, we turn to a beautiful formula that isn’t our words, but expresses our thoughts even better than we can.
Prayer books are like a tool. If you don’t need that tool, it’s okay for it to sit on your shelf… but when you do, it’s there for you, waiting.
So different prayer books serve different purposes, depending on what their contents are. There can be a prayer book of meditations on the rosary, for example— it’s easy to let your mind wander, so if you need to come up with x number of thoughts to focus on while another level of your mind is reciting prayers, contemplating prayers, and thinking about the mysteries in general-- that would be useful. Or there can be a prayer book with lists of prayers for different circumstances-- like particular novenas that are efficacious in different circumstances, different purposes, or have a particular history around them that is appealing. Or sometimes, we get into a prayer rut, and we need to expand— and so being able to flip around and do things out of the ordinary is a refreshing change.
Ultimately, there are (at least) four kinds of prayer-- petition, adoration, thanksgiving, and contrition. Any of those can be conversational. But if we were to find ourselves in a rut, or being dissatisfied with the inadequacy of our own ability to express thoughts or feelings, we can turn to the prayers in a prayer book.
But there’s no rule saying you need to use one at all. And just because you happen to own a certain one, doesn’t necessarily mean you’ll have a connection with it. Or, you might rely on different prayer books at different points in your path— I really liked my Raccolta when I was looking to get out of my rut and try different litanies and such that I wasn’t familiar with. But now that I have kids, I generally try and keep a few basics as part of our nighttime prayers, and change things up based on what month it is, to expose them to a bit more breadth. (ie, Souls in Purgatory in November, Precious Blood in July, Mary in May, etc.)
