Possibly nothing, depending on your specific needs, but it may depend on what else you're doing with your music.
In my case, I also want to have my music on my phone, which doesn't support FLAC. For the moment, I have enough space on my home network and my iPhone that I can leave the music of interest in AIFF format with no penalty. When I do start to run out of space on either one, I can consider ALAC, which has the exact same benefits as FLAC.
Some people have stated that the added computational overhead of decompression can be heard on a sensitive enough system, especially with hi-res files. Whether that is due to the added CPU overhead needed to decompress the files causing higher current draw which then creates more electrical noise, I don't know. I haven't had a reason to make the comparison in my own system.