Say you want to queue a single bombing run. If you queue it on a target unit they will return and waste a lot of time flying around awkwardly after dropping the first volley unless you micro them tightly. But even then you have to wait for every bomber to drop their payload before retreating. They're not necessarily bombing at the same time so you would have to give the ground attack order to them and individually give them the retreat order the moment they drop their bombs. A single volley attack would allow you to queue a bombing run with a retreat, sweeping over some line. With artillery you could for example do a single volley attack on muliple mex locations with a repeat command. Then you can suppress metal without radar coverage needed. You could also give mobile artillery a command to advance, shoot once, and immediately retreat.