-Xmx & -Xms parameters set memory. Here discussion would be done regarding such parameters that why they are used to set memory.
JVM i.e. Java Virtual Machine is produced in system memory, when Java starts. Execution as well as complete process of Java program occurs in JVM. Java applications have 64MB memory, by default.
In JVM, Xms is minimum heap size. If high sized initial memory is set, this might help a lot. Like, GC would be made to work