safemode: OFF ?

http://www.boonex.com/products/dolphin/doldemo/

quote from URL ^:
Your host must have any Linux/Unix OS (RedHat, Debian, FreeBSD, Mandrake, etc). NOTE: SAFE_MODE must be OFF, register_globals must be OFF.

My question:
How safe is it to set safe mode OFF? I read things about "you can hack a website when you set this option OFF.
Can somebody tell me more about this?

I read on a Turkish forum:
it's possible to make someone administrator from outside
functions like htmlentities(), strip_tags(), utf8_decode() must be controlled for security (?)

and safe mode must be ON, for every kind off treat ( i hope i didn't wrote this word wrong) :P