[Reeve of shinra]

Nevermind, ... I RTFM... lol

Posts are normally stored with bbcode tags etc. in the same form as the user posted them with so that it may be edited later, and then parsed at display time. By caching them, they are parsed at post time (instead of display time) into the HTML they will be displayed in and stored separately from the pre-parsed posts. This results in a faster display on threads, since the posts do not have to be parsed at display time.

This option determines how long posts are stored. While a post is cached, it will take approximately twice as much storage space since it is essentially being stored twice. If you have a busy site, and threads typically don't last very long, you can probably set this to a lower value such as 10 days. If you have a slower site, and threads typically last longer, 20 to 30 days might be a better choice. If you have the disc space, you can set this to a higher value for better performance.