The geometric algebra unifies many concepts from physics and mathematics that without it appear as a jumble of random unrelated things.
Using geometric algebra makes it much easier to understand and remember all those things and to predict relationships between them that are not obvious.
At least for me, learning about geometric algebra was the greatest leap in understanding the mathematical structure of physics. Only learning differential and integral calculus had a similar impact.
Without geometric algebra, you have to remember a lot of haphazard facts about scalars a.k.a. "real" numbers, "complex" numbers, "imaginary" numbers, quaternions, vectors a.k.a. polar vectors, pseudovectors a.k.a. axial vectors, pseudoscalars, tensors, pseudotensors, a very large number of arbitrary multiplication rules that give various kinds of products between all those entities and many other things.
With geometric algebra, it is possible to derive from a small set of easy to understand axioms all those kinds of mathematical objects and all the interesting kinds of operations that use them, without any additional arbitrary rules or definitions.
With geometric algebra, it becomes easy to understand not only why some mathematical objects are similar, but also why some that are superficially similar are nonetheless quite distinct, e.g. which is the difference between 2-dimensional vectors and "complex" numbers.
I have not found yet any book that I consider really satisfactory, mainly because all of them are more or less incomplete, which is understandable, because a complete presentation would require a huge amount of work for rewriting the manuals for all the branches of traditional physics to use models based on geometric algebras.
An older decent introduction is "Geometric Algebra for Physicists" by Chris Doran and Anthony Lasenby.
There are also several older books, which need more mathematical experience, by David Hestenes, who was responsible for the revival of the theory of geometric algebras, which had previously remained a niche domain of mathematics for about a century after the too early death of their discoverer, William Kingdon Clifford.
There are also many more recent books, which can be seen e.g. through a search on Amazon or other such sites, but I have not searched such books during the last years, so I do not know which of them are good.
The older books are good enough to provide an understanding of geometric algebras, but for practical applications one usually must go beyond them.
Even without applying in practice the theory of geometric algebras, it is still useful to understand it, because this removes most of the mystery from mathematical physics and it allows a more efficient organization in your head of the knowledge about it.