With gzip sizing is about the same, but processing speed wise it is not.
Same with csv data, for download size it really pays off to preprocess and pack into arrays of binary structs before compression.
This is part of a bigger class of effects in preprocessing data before compression, it is often surprisingly effective. For example delta coding or columnar format (SoA vs AoS) can yield big improvements depending on data.
With something that's grabbed once and cached likely forever I think the tiny bit of overhead for JSON won't make any difference. I've done this too and yes, of course a flatbuffer would be faster but the speed is just related to the initial download and caching. Beyond that you'd keep it in whatever structure is more efficient for the app to re-use.
Why would you pull in data from one format and keep it in the same format forever if it's not optimal for the device AND it doesn't need to be modified and sent back? Whenever I work on mobile apps and I have to cache data coming over as JSON or XML I store it where I can quickly re-access and NOT in its original format.
This thread seems like a conversation about how you can shoot yourself in the foot when it's very easy to avoid.
> I haven't heard of SVG renderers storing SVG XML files in a more efficient format.
Me neither. Sounds like it could be doable. Not sure how this related to our conversation though.
Also I think you have to pick something human readable here. One of the great things about SVG is that it's in XML so you can read it, tweak it, etc. It's super handy when you want to make small changes that only affect the image. So I see using JSON as pretty handy.
Don't forget there are many types of formats out there that have 2 types: a binary and human readable type. One used typically during debugging and one used for optimal over-the-wire transport. I don't see why this couldn't be possible at a later time.
Edit: I don't understand the downvotes. Over-optimizing is a thing. For a one time download I don't see the handfuls of milliseconds you're saving mattering. In either case of receiving a binary or JSON you will store it in an optimal format on the device...