In some marketing & sales industries (such as investment securities and financial services), it is becoming very important to note who initiated the contact (call); the client / customer, or the sales person (advisor). This information is important because it supports whether or not a transaction was solicited or unsolicited (a critical point in regulator supervision and/or litigation).
The "Inbound / Outbound" Call field may also support activity trends and analysis to track if a sales person is doing their job as an "outreach" person, or simply waiting by the telephone.
Some sophisticated telephony CRM integrated systems track the direction of the call by virtue of automatically displaying the contact record based upon caller ID. But for those of us who do not have access to such a system, manual tracking of this information might be very important.