When using FDE (full disk encryption) on a mac you might want to limit the users that actually can decrypt the disk. If that is the case then you might find the following commands interesting:

1) List the users able to decrypt the disk:

sudo fdesetup list

2) Remove a users ability to decrypt:

sudo fdesetup remove -user user.name

3) Add the user the ability to decrypt:

sudo fdesetup add -usertoadd user.name