The first round of combat is the most important many times. Depending on the situation, an attacker who gets diced in the first round might be better served to call off the attack losing mostly “fodder” rather than risking more valuable units in low/moderate probability attacks in later rounds. A single round can turn a lower probability attack into a very promising one without inordinate risk if there will be something left even if the first round goes poorly as expected.
A defender or attacker might choose to take a damaged BB as killed rather than keeping alive for the next roll. Both defender and attacker might consider their air more valuable in subsequent turns and write the ship off as lost. If one knows the attacker’s primary goal is to clear the fleet rather than trade air that both sides want to keep, then this “sacrifice” (vs an air unit) might make the attacker less likely to continue rolling. Likewise, even after winning the combat on the roll, an attacker might sink their own BB that would be left alone and easy fodder for a counter strike, rather than taking an air hit.
Then there are the questions of subsequent turn mobility that play out in complex ways. Sometimes leaving a blocker in a sea zone might outweigh keeping an air unit alive. A carrier might be kept alive in lieu of air if it is at a naval base and can be repaired and other air be flown in the next turn…or to its destination for an attack on that next turn. With multiple AC’s at least one will might be taken as a complete loss depending on where the various air has to land, how many air hits were taken, and what counter strikes are possible on the opponent’s turn.
Similarly, some mechs might be kept alive rather than arty if fast movers are needed for later turns and the arty can’t reach. Or an infantry and arty/tank/mech might be kept alive for fully filling a transport for the next hop rather than having two units left that can’t be carried on a single transport.
Single round calcs are useful for evaluating the likely cost/payback of a strafe…and the risk of taking a territory in the first round and ending up with the army out of position.