Caching Profiles web.config vs IIS

Question

What is the difference between configuring a Caching Profile in Web.Config and configuring it in IIS?

If you have this in Web.Config

<caching>
    <outputCache enableOutputCache="true" />
    <outputCacheSettings>
        <outputCacheProfiles>
            <add duration="14800" enabled="true" varyByParam="*"
                 name="AssetCacheProfile" />
        </outputCacheProfiles>
    </outputCacheSettings>
</caching>

And nothing configured in IIS in the Output Caching, will it work?

And what if you add all the extensions I use in Output Caching in IIS, what does that change?

It's a aspx page RetrieveBlob.aspx that uses this Caching Profile:

<%@ OutputCache CacheProfile="AssetCacheProfile" %>
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="RetrieveBlob.aspx.cs"
 Inherits="RetrieveBlob"  %>