You should disable Prevent account creation if you are blocking an IP you know to be used by multiple people who might not be responsible so they will not be caught in the IP block if they register an account usually except schools where  can be chosen as a block reason and where account creation would probably result in further vandalism Its whats called a softblock Another scenario is rangeblocking  if you have to block a range of IPs it might be a good idea to allow account creation for those users who were caught in the rangeblock Specifically for UAA it should only be used if you have indication the user chose the username in bad faith to disrupt or vandalize If you are blocking someone who just made a mistake when registering the name they should be able to register a new name HTH   To Juliancolton Nice tip of course but EasyBlock is not always flexible and an admin needs to understand SpecialBlock without it