Originally Posted by Chackonmanz
just wanting to know reasons on why not to have a too high php post size or a script memory usage.
Hosts need to limit each of those settings to a reasonable level to prevent abuse. If those settings are really high, a user could write a very poorly coded page and hog all of the resources on a given server, causing poor performance and reliability for other users on that same system.
When a host properly limits the PHP settings, a poorly coded script won't be able to hog as many resources, which leaves those resources available for otehr users. By setting reasonable limits, the host can provide better performance and reliability for all users.