Blocking a User & disabling him are two completely different actions. ‘Block‘ lets you restrict a user from accessing his Wakeupsales account, while your no. of users count still remains the same. You can unblock anytime you want.
Disabling a User has relatively stronger implications. Not only it restricts the user from accessing his account, it also frees-up a user space from your total user limit quota. So that you can invite another new member to your team.