No, it would be crazy for them to run things at saturation under normal circumstances as that does not allow at all for abnormal circumstances. The opportunity cost of not using something 100% all the time is offset against the worth of increased stability/predictability in the face of changing conditions.

Though you do need to define "saturation". Are you referring to bulk bandwidth or some other measure of throughput/goodput? Saturating in terms of raw bandwidth can reduce useful throughput due to latency issues.