I'm in a very close work relationship, and a growing friendship, with an INFJ.
When it's working — Expectations, predictions, reactions and plans are almost always the same. Not frequently; almost always. We often complete each other's sentences because our technical thought patterns are running parallel. There's virtually no energy spent translating and negotiating a foreign perspective, as would be necessary with another intuitive like an INTP or ENTP. As Enneagram Ones, shared anger in the form of normal work frustrations validates us, whereas with others we'd have to explain ourselves or else keep quiet. Mutual respect for security is understood as familial/collegial rather than practical; we want to look out for each other. Finally, we both value thoroughness and decisiveness, often working independently to overcome office inertia.
When it's not working — Secondary functions clash in more complex situations, and stress leads to ironic contrasts through tertiary functions. Both of us are equally tactful and outspoken, but I will more readily speak plainly and factually in search of clarity through debate, whereas the INFJ will use qualification and diplomatic redundancies to shepherd other parties. Tertiary interactions consist of a suddenly remote, imperious INFJ and a suddenly impressionistic, melancholy INTJ, and aren't of much use. Navigating an INFJ's needs and expectations in a friendship is daunting — sometimes I'm simply thankful to have seen the stark differences between each type. The INFJ is better positioned to perceive work and work relations globally, and "talk executive." By contrast, I have few qualms about high workload, unexpected situations, or challenges in execution.