Do you avoid sending unnecessary messages?

Sending an unnecessary Instant Message is a distraction to the person you sent it to. As the 5 word rule on emails, if your message is less than 5 words, e.g. "Great work!" or "Thanks!", it's probably not required.

Exceptions to this rule are when acknowledgement of the IM is required. We use IM in the office to notify that "John from F1 is on line 1." If the respondent doesn't say "OK - checking now" promptly we have to get up and go find them so John isn't left hanging on the line.

Another way to give an acknowledgement of understanding is to just "like" the message.