Your question depends on the stage of fermentation. If this is primary (very active) fermentation, disturbing the fermenting wort can be a good thing. It keeps the yeast in suspension and prevents stratification of the fermenting wort. Also the CO2 is very high in the fermenting vessel so the chance of oxidation is reduced. If it is later in fermentation (secondary fermentation), where CO2 generation is slow and yeast have been settled out, disturbing the wort would circulate hydrolyzed yeast products into the ferment as well as oxygen. Hydrolyzed yeast has a bitterness unlike hops and can produce an unpleasant taste.