There are use cases for lz4, I've had one in an embedded project. Slowish SoC (i.MX6 DualLite IIRC), relatively fast storage (eMMC - these tend to perform better than regular MMC). I measured boot time for the available kernel compression options and lz4 won by 100-200 ms or so compared to the next best option, which may have been gzip. It didn't make a big dent in overall boot time, but not bad for just setting an option. zstd, if available, which it wasn't, would have gotten a marginally worse result probably. IIRC, lzma was slower than uncompressed.