Essential Coding Theory [pdf]

interesting topic, but essential for who?

Essential as in "the essence of" not as in "necessary".

Programmers who can or want to work in lower levels of abstraction I suppose

It looks like you are thinking about programming and its abstractions. As somebody already pointed out, this isn't that type of coding. This is coding from information theory - source coding, channel coding, decoding, etc.

A lot of modern coding does involve programming. But it is more concerned with storage and transmission of information. Like how to reduce the symbols (in info theory parlance) required for representing information (by eliminating information redundancy), how to increase the error recovery capability of a message (by adding some information redundancy), etc. Applications include transmission encoding/decoding dats (eg: DVB-S, Trellis code), error detection and correction (eg: CRC32, FEC), lossless compression (eg: RLE, LZW), lossy compression (most audio and video formats), etc.

As you may have already figured out, it's applications are in digital communication systems, file and wire formats for various types of data, data storage systems and filesystems, compression algorithms, as part of cryptographic protocols and data formats, various types of codecs, etc.

"Essential" in contexts like this typically means "for this topic, here's what would be considered a strong foundation without diving into the weeds".

Friedman and Wand's Essentials of Programming Languages isn't 'essential' for everyone, even for programmers, it represents the 'essential' parts of programming language theory. If you read and understand that book you can have a serious conversation with anyone on that topic.

Similarly Essential Statistical Inference would imply a book that teaches you everything you need to know about statistical inference to do meaningful work in that area.

So the claim here is, assuming you want to understand Coding theory, then you'll be in a good place to discuss it after you read this book.

No, you’re actually just repeating what I meant. Applications that need those functionalities typically don’t have to implement those pieces of logic from scratch—it’s often consumed from a lower level library.

Oh! I see what you mean. In that case, the book is probably not targeted at programmers at all, though nothing stops you from pursuing it. Design of coding schemes is a discipline of its own. Sort of like writing a simulation software. Implementing the software will need programming skills. But the design of the numerical algorithms is more in line with physics and mathematics than programming.