The benefit is that you can manage many databases as one.
I suggest you read a bit more on the subject:
Start with the Concepts Guide: Oracle Database Online Documentation 12c Release 1 (12.1)
Several use cases are listed here:
I do not understand the point of the multitenant databases in Oracle (12c). Couldn't I always have many databases under Oracle (I have 11gR2.) Example, say I have a database for a store, a car dealership, a school, etc. Is that the same thing?
When would I have more than one installation of Oracle to care about multitenant? Use case? Thanks.
You can have more than one database on your server but what about managing the system resources for all those databases? How would you ensure that if there is anything like data dictionary which is duplicated in each database, doesn't occupy unnecessary disk space? How would oyu ensure that the background processes don't get duplicated and by some way, only one process, for example, would write the buffers for all the databases in their specific data files? The 12c Multi-tenant is meant for consolidation. By running many databases in a standalone manner, you are not consolidating anything.
I presented about the same topic in local user group conference. See if it helps in understanding the concept,
I think the point is to sell more for Oracle. People tend to minimize the downsides for specific sites. Cloud supporting sites may have different views on its worth. Here's some interesting comments: Kyle Hailey Why Data Agility is more valuable than schema consolidation.
I'm not so sure of this, Joel. I think multitenant might actually allow one to reduce the licence requirement long term. Sure, you pay: multitenant is an EE option (more expensive than partitioning, not as bad as RAC) but if you are running a twenty or thirty instances on one machine, consolidating them all into one with far fewer background processes might mean that you don't need as many CPU licences. This could be important in, for example, a DB Appliance where you can choose how many cores to activate. If the consolidation saves you a few cores, that pays for mutlitenant. It will take some time to know.
That's all dependent on how Oracle lets you define licensing, which, as we've seen in numerous examples over the years, is not exactly negotiable. Oracle can change it all on a whim.
Technically, I'm not convinced that the engineering to virtually partition redo streams isn't going to bite people. But that remains to be seen. I expect Oracle will slough that responsibility on to the customer with the customer being responsible for testing and Oracle drooling over the extra licensing for fails, whether during testing or implementation.