You really don't always need a high performing relational database.
Ask if you're making the right choice:
* When you don't actually need a database
* When you're not using structured data
* When you want pure analytics, or something other than a workload involving OLTP
* When you need to write to multiple nodes for a single database
* When your team wants a PAAS solution (lil pedantic on this, the hosted versions are slightly different)
* When your team needs a cheap solution
What do you think?