One of our server administrators set up 1 web site per web application. This is mainly to have different host headers per application. (We also create DNS entries per application, allowing the web application to be moved across servers without having to change links or bookmarks.) Is there any overhead or performance issues in doing this?

In other words, are there any major issues with having 500 websites with 1 web application each instead of 1 web site with 500 web applications?

One of our server administrators set up 1 web site per web application. This is mainly to have different host headers per application. (We also create DNS entries per application, allowing the web application to be moved across servers without having to change links or bookmarks.) Is there any overhead or performance issues in doing this?

In other words, are there any major issues with having 500 websites with 1 web application each instead of 1 web site with 500 web applications?

EDIT:

Let's assume each web site always has its own application pool. My question is really:

Is a web site just another configuration option with no overhead, or does creating many web sites decrease performance? (at all, even if it is minuscule?)