Capacity planning will help you determine how many partitions you need for your business and how much hardware you need in each partition.
You must perform capacity planning individually for each logical partition that you have or want on a server. Depending on the number of partitions you decide to create on your server, the primary partition may need more memory to successfully manage the partitions on the server.
See Capacity
Planning 
on the Logical Partition web site for more information. This information
can help you to determine the resources necessary to achieve a desired performance.