This sets the maximum amount of memory in bytes that a script is
allowed to allocate. This helps prevent poorly written scripts for
eating up all available memory on a server. Note that to have no
memory limit, set this directive to -1.
Prior to PHP 5.2.1, in order to use this directive it had to be
enabled at compile time by using --enable-memory-limit in the
configure line. This compile-time flag was also required to define the
functions memory_get_usage() and memory_get_peak_usage() prior to
When an integer is used, the value is measured in bytes. Shorthand
notation, as described in this FAQ, may also be used.
This is a quote from php documentation. Basically its gives your php scripts access to as much memory as they need. Probably not good practice. But there you go.