Does the "purge" command damage any thing in my system?
No harm will come to your system through using the purge command. The purge command clears out pages which have been written to memory which the system thinks it may need again. Usage of purge can cause some applications to temporarily run slowly if resources need to be reloaded.
From the purge man page for Xcode 3.2.5:

DESCRIPTION
Purge can be used to approximate initial boot conditions with a cold disk buffer cache for performance analysis. It does not affect anonymous memory that has been allocated through malloc, vm_allocate, etc.