Right, there are some extreme cases (lxd, multipass…) where it would probably make sense to ask/warn about potentially huge snapshot (not doing automatic snapshots by default because of extreme cases isn’t a good idea IMHO; for users wanting that there is always “snapshots.automatic.retention=no” config option mentioned earlier).
FWTW, there are some other improvements in the works such as not attempting an automatic snapshot if disk space is low and doesn’t guarantee successful operation.