The application objects (such as shells, companies, and so forth) are stored in the Java Virtual Machine (JVM) Heap. Most of these objects are short-lived and are periodically cleaned up by the JVM garbage collection mechanism.
As the concurrent users increases, the number of objects in Heap increases, and performance and scalability will be affected due to the congestion and resulting higher frequency of garbage collections.
Increasing application JVM Heap (with adequate physical memory provisioned) is an efficient way to achieve the desired performance and scalability. See the Deployment Categories section of this guide for guidelines on configuring the optimal Java heap size.