Other then $cr and $lf being preserved what other purposes does saving a hash in binary offer?

I think that's the only benefit a binary file offers.

Anything a &binvar offers, I guess. Like preserving multiple spaces, too. But I'm not really sure if they'll be preserved when loaded as well.

Saving/loading a hash table as text will preserve spaces. The lack of consecutive spaces is a quirk of mIRC involving space-tokenizing lines given to it via the command line or a script file, but since each value of a hash table is saved and loaded internally the consecutive spaces aren't stripped.

It also preserves NULs (ASCII 0s), which is useful if you need to use a binary file in your script correctly.

Unfortunately it doesn't

//bset &a 1 65 0 66 | hadd -mb table item &a | echo 3 -s $hget(table,item,&b) : $bvar(&b,1-) | hsave -bo table table.hash | hload -b table table.hash | echo 4 -s $hget(table,item,&b) : $bvar(&b,1-) | .remove table.hash