It would make sense to put a small database size limit to make sure queries run fast.
If you’ve got a 10GB database, it’s easy to make sure every query runs blazing fast.
Throw hardware at the problem, throw a lot of indexes at it, and you’ll get good performance.
Keeping things small also makes backup & recovery easier, and makes high availability design easier.
There are no SQL Azure RAM limits or CPU limits.
You have no control over how much CPU power or memory your database gets.
SQL Server 2008 has a Resource Governor that allows database administrators to throttle queries based on login or database, but Azure doesn’t support those features.