[Moru]

It's mostly subdomains since windows can't use wildcards (*.domain.com). Setting up such a large hosts-file might slow down your computer a bit though.

There are some tools that lets you run wildcards in the hosts-file but can't remember the names at the moment.

[nielsbjerg]

Again, a tool concern. Not trying to downplay the possible solutions, but rather bring attention to the magnetude

[Moru]

I'm not sure what you mean, I see 13 different domains in that list, the rest is subdomains of the same 13 domains. You can't count that as "sheer amount of domains". Our company probably have 2000 different subdomains on 5 domains? Subdomains we can create as we want to, it's just some letters before the domain part of the adress. Eg: Subdomain.Domain.com. That is what the wildcard is for, *.Domain.com catches them all no matter how many extra we create. Wildcarddomain is needed for example on an SSL certificate to accept any subdomain for the domain you ordered.