Bans are a type of punishment given to players who perform illegal activities within the game such as hacking and duplication. All bans exist for a purpose, there are no bans without a purpose. If you are banned then you have performed an illegal action within the game. Not all bans are permanent.
Types of Bans
There are many different types of bans within the game, some of them work differently from one another.
Ban from duplication is the most common ban that exists, there are many ways of duplication that you can get banned from.
Duplication cannot be detected by the game, so the player is typically not banned the first few times they duplicate items. However, if obvious evidence that one is consistently duplicating is sent to Defaultio in some way, they will most likely be banned.
Rarely, Defaultio may join straight into the server of a duper just to add a message to the ban. The reasons for why Defaultio sometimes does this is because he may gain knowledge on how a duplication method works by allowing the player an unban if they tell him (usually, with all Duplicated items deleted). Defaultio needs to know how dupes work so that he can patch them.
Ban From Hacking
This is another very common ban. If the games exploit detector detects the player, hacking it will either ban them from the game or kick them from that server depending on how to severe the exploit is. The player can also be banned manually if someone catches them hacking (and tells Defaultio about it.)
Hacking is also against the ROBLOX Terms Of Service; few bans may be issued by ROBLOX instead of Defaultio.
Exceeding the Money Limit
This type of ban was extremely common. Essentially, if a user had exceeded the cash limit (20m) then the game auto detected if the user had too much money and then proceeded to ban that user. The reason you were banned for having too much money is because that it is typically almost impossible for a player to gain over 20m cash considering how long it would take to obtain it.
Note: this feature no longer exists
Ban From Scamming
This type of ban is not as common as the other bans, but it exists. Although the game cannot detect if a player is scamming, players who witness it can send evidence to Defaultio. Sometimes, not often, he may ban the player for repeated scamming.
The Auto-Ban System
In the game there is an auto-ban system, which is able to detect the quantity of an item on a base, how much money someone has, when someone is hacking, etc. The auto-ban system isn't 100% perfect; it doesn't ban all users, and may sometimes unfairly ban those that simply have too many of one loose item on their base. The Wiki suggests that the player keep the number of loose items (especially gifts) on their base at a minimum to prevent this. These bans usually last 2 weeks.