The main reason to land on multiple beaches was for logistical reasons. The Allies needed to land as many troops as possible on D-Day, to ensure that any German counterattacks against the beachhead could not push it back into the sea. The first waves of the landings consisted of six infantry divisions. To this must be added the additional reinforcements to the divisions (such as the specialised tanks of the British 79th Armoured Divisions, the Rangers at Pointe du Hoc, or the British commandos) and the follow-on forces. By the end of the day, somewhere in the region of 133,000 men had been landed across the five beaches. Trying to fit this many men into the frontage of a single one of the beaches would have been impossible. There would not be space for the craft to land them. The beach would quickly devolve into a massive traffic jam, a perfect target for German artillery, because the exits would not be able to take this many troops. Landing this many troops required a broader front.

Of course, the beaches used on D-Day were chosen to only have enough space for a single division to land - though Sword and Utah were smaller, being roughly half the size of Gold and Juno, while Omaha was assaulted by elements of two divisions, but was a similar size to Gold. We could expand the width of our hypothetical single beach so that all five divisions could fit onto it simultaneously. However, this runs into geographical, rather than logistical issues. Not every length of beach is suitable for an amphibious assault. It might have rocks or sandbanks offshore that make approaching it too dangerous. The slope of the beach might be too steep or shallow for landing craft to beach properly. The material of the beach might be wrong for tanks to run over - it might be too soft to support their weight, or composed of pebbles that gum up the tracks. There might not be enough ways off the beach and inland, due to cliffs or swamps behind the beaches. The German defences might be too heavy, making a landing too dangerous. Trying to find a length of beach suitable for a landing by five divisions would be incredibly hard; the smaller beaches actually used on D-Day were often constrained by one or more of these issues. The length of Sword Beach was limited on the left flank by the mouth of the Orne and mudflats, and on the right by rocks offshore around Bernieres. Omaha was overlooked by bluffs, which aided the German defences and limited the number of exits, while Utah's exits were limited to a few causeways across terrain the Germans had flooded.

Another issue is that the beaches had to be widely spread to allow for a wide range of objectives to be taken rapidly. The assault was defined by two logistical hubs - the major port of Cherbourg in the west, and the road and rail hub of Caen in the east. Taking the former quickly would allow the beachhead to be supplied much more easily, while taking the latter would greatly complicate German counterattacks against it. The need to capture both towns quickly set where two of the beaches had to go - one had to be as close to Caen as possible, the other had to be on the Cotentin peninsula, putting troops into a position to move on Cherbourg quickly. These were Sword and Utah - but these two beaches were separated by about 70 km (40 miles). The other beaches were needed to fill in the gaps and secure appropriate landing sites for supplies to support the beachhead until Cherbourg had been taken. Gold Beach aimed to secure the villages of Port-en-Bessin, which would be used for landing petrol and oil to supply the Allied tanks ashore, and Arromanches, which would be home to a Mulberry harbour (a prefabricated harbour used for landing supplies when no real port was available). Juno would secure the links between Gold to the west and Sword to the east, as well as the small port at Courselles. Omaha would prevent the Germans driving a wedge between the British beaches and Utah, as well as providing a second location for a Mulberry.