It's a hex dump, in a fairly common hexdump format, with each line of output containing the byte offset (in hexadecimal\*), hex digits for 16 bytes, and the ASCII representation of those same bytes.

\* Note how the byte offset increments by 0x10 hex (16 decimal) for each line.

From `man xxd`:

> **NAME**
>
>        xxd - make a hexdump or do the reverse.
> 
> **SYNOPSIS**
>
>        xxd -h[elp]
>        xxd [options] [infile [outfile]]
>        xxd -r[evert] [options] [infile [outfile]]
> 
> **DESCRIPTION**
>
> `xxd`  creates  a  hex  dump of a given file or standard input.  It can also convert a hex dump back to its original binary
> form.  Like `uuencode`(1) and `uudecode`(1) it allows the transmission of binary data in a 'mail-safe' ASCII  representation,
> but has the advantage of decoding to standard output.  Moreover, it can be used to perform binary file patching.
> [...]

hex dumps are extremely useful when you need to know exactly which bytes are in a file at some exact location.  They can help to diagnose problems where, for example, there are unexpected bytes (e.g. NULs (`0x00`) or carriage-returns (`0x0D`)) in the file and, as @ilkkachu mentions in his answer if the binary file format is documented (or you happen to know it anyway), it is often possible to interpret specific meanings to bytes in specific offsets (locations).