Partitioning is a religious subject. Usually partitioning considerations are driving by the wish to prepare for the future.

Generally you want to:

• Make sure that if you run out of diskspace you application will keep running where possible

• Make it easier to extend diskspace in the future
  

Best you can do to protect against running out of disk space is to put /var/log on a separate partition.

To make it easier to extend disk space is to use LVM while partitioning, because in that case you can add another harddrive, and add that to your database directory. This does not do you much good on a cloud instance, but there you can just upgrade your subscription.

In short: if you own your own server, be sure to use LVM, and put /var/log on a separate partition.