Fast and Efficient but a serious downside
Yes it was fast, not as intrusive as a phone call not as likely to be missed or delayed a email.
The serious downside however is tracking. Actually lack thereof. When used with clients, issues, followups, requirement changes and other critical information was lost. When used internally not only were the same items lost but discussions leading to design decisions, assignment of action items and other critical information was lost. At least with email the item or thread can be cc'd or forwarded to responsible parties. Chat or IM in an enterprise setting without logging and tagging leads to (usually unintentional) bad practice and loss of critical information.
~GeoD
