What is a word that means when people only contribute or speak when they have something of merit to say or add?

Solution 1:

pertinent

: pertaining directly or significantly to the matter at hand; relevant (Random House Kernerman Webster's College Dictionary)

apropos

fitting and to the point (American Heritage® Dictionary)

pungent (or poignant)

: being sharp and to the point (M-W)

Solution 2:

People who contribute something useful are being constructive.

Solution 3:

I believe I found the word: compendious