The regexes work by compiling their strings into the equivalent Rust code on creation. For performance reasons, you are advised to reuse your regexes instead of creating them anew every time you use them. A good way of doing this is by using the lazy_static crate, which we will look at later in the book, in the Creating lazy static objects section in Chapter 5, Advanced Data Structures.
Be careful not to overdo it with regexes. As they say, "When all you have is a hammer, everything looks like a nail." If you parse complicated data, regexes can quickly become an unbelievably complex mess. When you notice that your regex has become too big to understand at first glance, try to rewrite it as a parser.