I have Internet Mail provider active. The reason is that if you happen to get infected with a malware that sends out email from your computer, this provider will let you know that this is happening. Otherwise, it may be some time before you know this is happening … perhaps not until your ISP send you a warning that you are sending out too much email, that your are a spammer, and that you may loose your connection privileges. Running this provider uses very little resources and can save you much grief should such a malware gets on your computer.
Yes, it is ok to leave the other 3 providers off if you are not using IM’s, Outlook, nor P2P. Just be sure to turn them on in the future if you decide to use such services.