Salesforce specifically? Global availability for 1000’s of users simultaneously. While integrating with mail and VoIP services are easy ones off the top of my head. It’s extremely expensive but a hidden cost on top of that is actually configuring and maintaining it well. The initial fine-tuning for large orgs will take years for example. But if it’s done it’s actually a joy to work with, especially if you switched from a half-baked solution like a graphical shell over a FoxPro database or something.

At a previous employer of mine the helpdesk side was integrated to it and it was brilliant. All calls and mails were autoregistered and after using it for a while more and better answer templates were included. (Templates we could modify with situation specific parts as well) The template approval process was another great example as technical experts from different continents were part of a review committee to make sure only good solutions were allowed, and after that local experts could add translations of the templates.

I’m sure there are many things morally wrong with Salesforce the company, but a well implemented instance of it is a dream to work with.