lz4 is pretty fast so the latency is not relevant actually but you could even switch to lze. The only reason to use compression is to shorten the records. E.g. if you have a 2.3MB file and 1MB recordsize then you’d need 3 records to store that file. Then you have 3MB of used space, even though that file is only 2.3MB. With compression that last record would be shortened to 0.3MB. That’s why I have a compressratio of 1.3 on my latest node dataset with 512K recordsize.
Apart from that you are right, you shouldn’t be able save any real space because the data is encrypted.