What minifying removes
Whitespace between tokens, indentation and line breaks. That is all of it. JSON has no comments to strip and no syntax that can be shortened, so the saving comes entirely from formatting.
The saving is larger than people expect on deeply nested documents. A four-space-indented file ten levels deep can be forty percent whitespace by weight, and that whitespace is paid for on every request if the file is served without compression.
When it is worth doing
For a file served over HTTP with gzip or brotli enabled, minifying gains very little: the compressor already handles repeated spaces efficiently. The place it pays is where compression is not available or not applied, such as a value stored in a database column, a message on a queue, or a payload counted against a size limit.
For a file a human will read, do not minify. Keep the readable version in source control and minify at the point of use.