30secs and shorter, I think going all out makes sense even if you fade a bit by the end and don't hit the same power for every interval. Those intervals are about building explosive power, not aerobic conditioning.

For longer intervals (even "short" VO2Max intervals in the 3:00 range) pacing is more important as it's about time in spent in the training zone that produces the adaptations you're after (eg VO2, threshold/FTP, tempo, etc).