TEAM shipment means that in team games everyone on your team benefits from your shipment. Typically, they are not as good as non-TEAM shipments, per person.
For example, a normal mill card might give you +20% mill gather rate. A TEAM mill card would give you a +10% mill gather rate. So, the benefit evens out with a 2-person team, and goes ahead with a 3-person team (the team as a whole gets 10%+10%+10%).
Of course, their usefulness assumes that the entire team is using a strategy that would benefit from the card. Often, that isn't the case.