When this caching time is set, IIS will hold the module content unless it's updated by an editor (at least this is what I found).  I didn't notice much difference, and what eventually happened is a lock up of the page.  We didn't didn't set IIS to clear the old cache so every 1000 secs, the contents would be added and added to the cache until it was full.

In other words, be sure to set up IIS properly before you use this cache time setting.  Then see what any differences are.  If this isn't possible, try keeping the number of modules down on each page.  That will decrease the number of database hits on each page load.