Why are the shmmax and shmall defaults very high in Red Hat Enterprise Linux 5 and 6?

Issue

• After installing RHEL5, the system sets up kenel.shmmax and kenel.shmall with high values using sysctl.conf :

  #cat /etc/sysctl.conf
  
  [..]
  # Controls the maximum shared segment size, in bytes
  kernel.shmmax = 68719476736
  # 68719476736/1024/1024/1024 = 64,so that means maximum segment size is 64 Gi Byte.
  
  # Controls the maximum number of shared memory segments, in pages
  kernel.shmall = 4294967296
  # 4294967296*4096/1024/1024/1024 = 16384 Gi Byte 
  [..]