I think there's always a question of "when to hold back" and "when to support". For infants past 5 months old, I always encourage to hold back a bit, and provide opportunities to self soothe/resettle to sleep. I'm not saying to CIO or CC, but not to rescue. Sometimes, simply placing a hand on the back while he/she fusses is helpful. Other times, if it sounds like just a protest or settling into sleep type of fuss, then I tend to hold back altogether.