Pros and cons of sending confirmed griefers to a jail!
Pros
* It's often more amusing for the normal players than simply /kickbanning them.
Cons
* Thanks to commands like /home and /warp, you'll also need to install a jail-related plugin for this, or DDR would have to make a new usergroup that doesn't have any permissions- this would include placing/breaking blocks. That being the equivalent of the "Banned" usergroup, you may as well just type /ban [name], /kick [name] or /kickban [name] if this server has that command. While a person with no permissions, including placing/breaking blocks, can't seem to do much, they can still try to be a thief and a...
* Chat spammer. If they can't get to you by destroying your stuff/stealing from you, what will they do? Disrupt your conversations. If there's no /mute command for the moderators of this server, be prepared to kick a griefer within thirty seconds of sending them to the jail, since it likely won't be long before they start spamming gibberish or a single letter to constantly try and fill up the chat screen. In the event that a spammer is jailed and there's no /mute command on this server, this negates the one and only "pro" there is to jailing people; it's hard to find a griefer being jailed amusing when they're a spammer, too.
* The possibility of escape. It would only be a matter of time until another update breaks the plugins keeping them jailed, and once broken, that would open up the possibility for them to escape. What first brought this thought up was the suggestion to have the jail be in the Space world; the moment they jump to their death to kill themself, unless there was some special spawn set up just for them, they'd respawn in the normal world, ready to continue griefing again. By /banning and /kicking someone, there's no risk of them escaping, then stealing from various chests and such.
* The mindset. "Oh, they haven't outright banned me; they're not even kicking me! They must want me to stay on the server." With that mindset, if they didn't go with the, "Welp, I guess I'll be a spammer since I can't annoy them in any other way now" route, eventually, they'd be asking to be let out, telling you that they have nothing but the best intentions, that someone else did all the griefing or that they're "really sorry," etc, etc. (Funny how they mention, "lol ya im sry now unban mee" after they constantly denied doing any griefing for 30+ minutes straight, only admitting to it after they're facing consequences for it.) It's not so much the annoyance factor of, "Yes, we heard you the first, second and twentieth time, plus all the times in-between: you want to be let out/unbanned. We get it," it's the possibility of a kind-hearted moderator thinking to themself, "Well, I guess they HAVE been in there for a long time now... Y'know, maybe they really didn't grief, despite BigBrother saying otherwise/Sure, they griefed, but maybe they really did learn their lesson by sitting in time-out for awhile; maybe I can trust 'em," then letting them go free, only for that griefer to repeat their actions.
One of my favorite quotes would have to be, "With a more definite method of victory on hand, what need is there to choose a hazardous one?" and I believe it applies strongly to this situation. Why take all these risks with /jailing someone when you have the risk-free /ban and /kick commands at your disposal?