They that control work entry, control the world!  While the statement is a bit grandiose, controlling work entry has a huge impact on both the value a team delivers as well as its physiological health.  Not allowing overt control of work entry though saying yes or no (or their alter egos, now and later) turns teams into liars. Yes stops being an affirmation or decision to proceed with any alacrity.  Three non-yes yeses are:

Yes as a temporary accommodation.  A few years ago, Anthony Mersino pointed out in a conversation that saying yes deflected the pain of hard conversations until a later which may never come. This scenario offers a temporary sense of peace which is later overtaken with stress and apprehension. Allowing an open tap of work entering ends up undermining trust in the long run as the backlog and/or work-in-progress builds up and delivery slows down.  

Yes as a form of passive aggression.  We have all heard someone express a positive affirmation tinged with sarcasm. This type of response is a way of avoiding having the hard conversation about controlling work entry while expressing deniable (sort of) displeasure. Simply put, this type of behavior is a crutch to avoid authentic conversations. 

 Yes as a form of egalitarianism.  What a team works on should be a reflection of a meritocracy based on value. Accepting all work without regard to value disrespects the needs of the organization and the stakeholders requesting the work.  The lack of transparency generates discomfort and stress for everyone involved in the process.  

The ability to say yes or no or even now or later and to have those answers stick empowers the team and their product owner. Having a backlog that reflects the needs of the product and organization is a form of transparency that reduces the stress on teams and doesn’t force them into a position of having to say yes when they really mean no.