You can spend a lot of time in Second Life building and scripting to create all sort of cool and original objects, also there is Linden dollars to be made by selling these object in the SL marketplace. Permissions are a very useful way to help protect your creations, specifying how other players can handle your object such as copying or modifying. Without things like the transfer permissions people could simply buy an item from the marketplace, then resell the item for a cheaper price than the original creators.
In my opinion SL have the protection of intellectual property well covered. Although I am not aware how much of a problem plagiarism is in SL, I think the only additional way to improve protection would be to have a system where it could compare how objects are made to stop people building a replica of your idea.
CopyBot is a programme that was developed by the Second Life team, which allowed them to export an object from SL for backup reasons. They then released it to the public, people then modified the code allowing them to export backups of objects that were not theirs basically overriding the whole SL permission system. You can imagine the problems this caused for creators, so SL announced if it was used for this the player would be banned.
Through the correct use and understanding of SL permissions you can easily control how your creations are modified, transferred and copied. However, with programmes like CopyBot it is still possible for people to steal your creations, because of this Linden Labs have the Digital Millennium Copyright Act (DMCA).
If you notice that some has stolen on of your creations, this could be through seeing it in SL or just on the marketplace. You can contact Linden Labs who will assess the object under the DMCA, if the object is found to be copied/stolen they will delete the object and possibly ban the player. The only down fall is there is no way to stop the player from making another account and doing this again if they have the now how.