The ground crew may add to a photo or distract. This question can be extended to what is behind the subject. Evidence of airshow paraphernalia, tents, ropes, people in civilian clothes, handbags, prams, kids, litter and just about any other FOD material that goes with an airshow will detract from the subject. If the opportunity to take pictures from an elevated perspective arises, go for it. Some aircraft like the Hornet hide portions of markings when taken from three quarter front.
Some airlines have registrations in hard to see places.
Each aircraft type has a varied appeal from different perspectives. If there is enough to cast a dark shadow with a definite line, then shoot. The sun should be generally behind you, casting your shadow generally toward the subject. My rule on late in the day sun is, if your shadow is longer than you are tall, then think twice if the subject is worth the film expenditure. Avoid the high noon sun shots.