Assuming this is for an internal community at an organization that is at least mediumly entrenched with email, the alerts can be a great way for people to stay in touch with what's happening with the community.
I have heard very few complaints about the "noise" and of course users can opt-out of receiving emails if they wish.
While I have heard many complaints about noise from emails, those same people assure me that they would never want them all turned off. I would proceed with extreme caution in turning off emails. Many people are just not ready to NEED to log in to get their information. It is not what they are used to. We've been at this for 4 years, and there would be a revolt if I ever suggested turning off emails.
Myke created a lot of documentation and continues to raise awareness on how to manage notification preferences, especially after upgrading to Jive 5. Ultimately this is all a training issue and adoption campaign. True dialogue:
User: I get so many notifications and email now from Nation (our internal community).
Myke Mansberger: How did you receive the information before?
User: They would email me or the everyone distribution list.
<thoughtful pondering moment>
Most of the time, users think we are introducing more emails or noise when in fact we are giving them a powerful communications tool to manage the inbound messages. Don't shoot the messenger, filter the message. Sometimes we have to state the obvious.