By both inclination and training I prefer tactful but direct and unadorned truthfulness in communication. If being overly polite means the work suffers--which happens more often than I ever expect--I'm ready to dispense with polite. The trick is that one can not unilaterally decide to dispense with "polite" and expect one's interlocutors to come on board and respond in kind, putting the work first, and feelings second. Tact and politesse are thus crucial in any new working relationship. What can help relationships sooner reach truthful communication is experience and training in the field. The more experience and training in the field everyone has, the more they're interested in getting down to brass tacks.
Favoring efficiency and truth in working communication does not mean turning cruel or selfish. In critics, for instance, I value honesty but not inane cruelty. Among Philadelphia critics, Toby Zinman is always honest and can be very smart but is frequently lazily cruel, choosing the easy one-liner over more informative analysis. Neither efficiency nor truth require abusiveness by either critics, directors, actors, designers, stage managers, carpenters, or producers.
I've come to value working in ensembles with which one does more than one show over time because a context evolves for honesty and efficiency and putting the work first. This was especially true in grad school where we were learning how to do just that. When I get the opportunity to produce or co-produce my own work one of my goals will be to create an ensemble in which there's enough trust to get down to making art. My experience is that being polite is not a sufficient condition for trust to emerge. Truthfulness is necessary, too, born of an instinct to always-work-better.