If you’re compressing it anyway why turn it into base64 or ascii hex? The compressed data will be binary anyway, so just compress the input data directly.
One example are JSON/XML/HTML responses over HTTP: you need the 8-bit ("binary") data in an ASCII format to fit into JSON/XML/HTML, while HTTP provides gzip (or DEFLATE, Brotli, etc.) compression over the whole response if both the client (by including the "Accept-Encoding" header in the request) and the server implementations support it.
Correct, we're sending data points as typed arrays inside a much larger JSON payload.