When adding a new website to IIS, the Binding section requires the host name, and gives an example as:
Example: www.contoso.com or marketing.contoso.com
When creating my website for zuggler.com, when should I include the www prefix?
Note that I will most likely use my web.config file to redirect zuggler.com requests to www.zugger.com.
Does it make any difference if I include the www prefix in the Host name box when creating a website?
In essence, you don't need to provide a host name here, however if you do then clients must use that hostname. If you are redirecting from zuggler.com to www.zuggler.com and you want to add a host name, you only have to enter the latter. If you want people to be able to type both without redirecting, then you have to add two bindings as per below.
From TechNet:
I would add the binding with the www. hostname, by default I always do it for some reasons;
1) If you add later a SSL certificate it must match your hostname. the www. is likely to be used there, unless you buy a wildcard SSL certificate.
2) On the HTTP/1.1 RFC and later (https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html) the browser always send the Host header to the remote server, thus the website in IIS without a hostname binding fallback to be used only if someone use the direct IP, or if only one website is hosted on your IIS. (but that break the point 1)
So you could use the www. binding, and leave the one without binding to redirect to that one.