A higher Hub capacity lets you run more modules
By now you probably know that you should increase your Hub capacity 
and run more instances of the 
same application server when you 
want to support increased traffic on your interactive site.
You should also increase your Hub capacity so that you can run more 
instances of different application servers.  Here are examples of 
situations that warrant this:
-  Extreme bottlenecks
 If your average page creation 
time is half a second, but one page takes 5 seconds to run because 
it is waiting for a slow back-end process, it is highly beneficial 
to isolate that slow page in a separate EXE.  Examples of slow 
pages include: running credit card charges, certain database queries, 
generating Adobe PDF files, and system administration features such 
as importing new database content.
 
-  Major functionality divisions
 Just as Delphi lets you 
use datamodules and forms to divide up your project into multiple 
work areas, WebHub lets you divide up your project into multiple 
AppIDs that work together to service a web site. While it is not 
necessary to divide your application into modules, you may find it 
much more convenient to code this way.  Examples of modules might 
be SEARCH, SHOP, DELIVER, and ADMIN.
 
-  Phased project development
 Like any software development 
project, web sites are generally built in phases.  You might build 
one application per quarter, and leave the prior ones completely 
intact and unchanged.
When you build a WebHub site, you can start with everything all 
in the same application, and if you find it's getting too slow or 
too crowded, you can then make the separation.