When git annex does fsck on (for example) a GPG-encrypted special directory remote, it first transfers the whole file into .git/annex/tmp directory. If your annex is on an SSD, it's a good idea to make .git/annex/tmp a symlink to say /var/tmp so SSD isn't worn down. This actually may be a better default.
If .git/annex/tmp is a symlink to another fs, then adding doesn't work:
It looks like it would be good to have two types of tmp directories here, one for adding, another one for verifying (and that one could be redirected off SSD).
fsckon the (encrypted) remote itself, as it would avoid to clutter either the network or the tmpdir. However, that requires some changes in git-annex's backend. Indeed it would no longer be enough to store a single digest per (plain) file: a new digest needs to be stored for each encrypted copy. It is not necessarily a big deal, but the backend would need to be reorganized carefully.