Boyd's technical writing is unrivaled in its clarity, in my view, and motivated much of my writing as a professional scientist communicating mathematics. This is his seminal work (though Boyd's Introduction to Applied Linear Algebra is also a must read), and it shows. The book is partitioned into three parts (Theory, Applications, and Algorithms), and opens with a brief but surprisingly insightful bird's eye view of mathematical optimization per se. Boyd's views here I think have withstood the test of time, and are not in conflict with the onslaught of nonlinear programming methods popularized in modern machine learning (which are often now the only methods taught and/or understood by students in computer science departments). If one reads this book cover-to-cover, I feel confident she comes away with a perspective much like the following, which I think is true to Boyd's personal views, and much of the ethos of this book.
In many, many applications of interest, framing it as a convex optimization problem garners an enormous improvement in effectiveness (let's say, the first 85% in improvement of your problem's objective, as a semi-arbitrary number). It is possible to improve even further with nonlinear programming methods, bespoke application-specific insight, etc., but very often a strong foundation in the methods contained in this book reward the applied mathematician with significant improvements over non-systematic methods (hand-designed solutions from earlier eras, unjustified heuristics, etc.). There are surely problems that do not exhibit this character (maybe next-token prediction, although it would be interesting to see the reduction in performance using a convex method), but this is a good general rule for the practicing scientist/engineer.
This book will enrich your understanding of a vast array of techniques split across dozens of fields (with their own idiosyncratic terminology): statistical inference, information theory, signal processing, electrical engineering, machine learning, etc. In many ways this books contains much of the "kernel" that underlies many related ideas across all of these fields. One leaves with a sort of liberated and unified view of much of what is going on, and strong intuitive ideas that allow one to predict when certain techniques should be expected to work (and how to justify that they do).
The first section on theory is in a word: tight. That is not to say, terse, or lacking in generosity (in fact, Boyd is one of the most generous mathematical writers), and it is in fact extremely possible to understand with just a basic familiarity with calculus and linear algebra. Many well made figures and examples clarify the core ideas, and the final chapter on Duality is a real Tour de Force that beautifully simplifies the blasted Langrange multipliers taught in high school calculus, the KKT optimality conditions, and importantly, the trifecta of the analytic, geometric, and practical relationship between the primal and the dual.
The second section on applications is extremely empowering. After spending a few weeks fighting hard through section one (not because of dryness or poor writing, but because of the depth and subtlety of the ideas), this is the payoff, and it is sweet. Approximation and fitting (with a side tour into probability theory and statistical interpretations), is a better treatment of the topic than is taught in most other field-specific works (e.g., on statistical inference or machine learning, though some signal processing texts do ok). Statistical estimation is similar, and really served to simplify and unify much of my views around statistical inference, hypothesis testing, and detector design. The geometric problems are both fascinating and extremely useful in practice.
The final section on Algorithms, is, as flagged in the introduction, not a treatment of SOTA methods or serious computational considerations. Boyd writes that "we have chosen just a few good algorithms, and describe only simple, stylized versions of them (which, however, do work well in practice)" which is true to form. I was able to spin up a simple (but reasonably reliable) interior point method just from the content in this book, but a serious implementation would require more support and backing from Golub's Matrix Computations, a copy of Numerical Recipes, etc. This is not a downfall and is perfectly well advertised within the first few pages of the book. The section absolutely delivers on its promise of introducing the important ideas underlying how these algorithms work.
If a scientist or engineer can tolerate only a single "mathematically-oriented" book, this is a great choice. The fact that it's freely available online, with a truly priceless lecture collection posted on YouTube (where one can enjoy the uniquely powerful teacher that Boyd is, and benefit from his side commentary and stand-up comedy), don't weigh toward the quality of this book, but should be noted nonetheless. Boyd is nothing short of the GOAT.