The 3 directly introduces the people factor into the communication. There is no need to specify this in all situations since people are almost always involved. The 3 need only be included when there is a direct emphasis on people.
 

• 31 I or we
• 13 you (singular or plural)
• 33 they, or people in general
• 73 the person specified
• 32 the operator
• 326 meeting
• 386 person in charge; the boss
• 233 users of a system or service; consumers
• 473 human error
• 83 pleasurable
• 53 who?
• 63 reaction to an idea
• 493 time wasters

In general the 3 should be used sparingly. It is only necessary when the people factor is a key part of the communication. That there happen to be people involved is not sufficient reason for including a 'people factor'. You might as well specify daylight or night-time whenever an action is mentioned. Some things can be assumed unless they are central to the communication.