if you have the intention of ever competing in utility, all signals with one hand is harder for a dog to discriminate because all the motions essentially start the same and it leads to a lot of unnecessary confusion when you start working at a distance. whatever hand you want to use is fine, i use my right arm for drops/downs, left for sit, and right for recalls. i also have a stand command with BOTH hands, depending on if i am in heel position (use the left) or in front of them (use the right). utility is always down, sit, come - and most people have too similar recall and down signals and its confusing for the dogs even up close. dogs can absolutely do it off one hand no problem, but its certainly EASIER to teach alternating hands.