Orvet, the various WWII German daggers (SA, SS, etc) were designed after the earlier Swiss "Holbein dagger," which in turn descended from the baselard. In Swiss history, they were usually paired with a katzbalger (or occasionally a kriegmesser, or both). Right about now a few folks are wondering how the design got to Germany, and why it matters. . . .
Way back about 1485-1490, Maximilian I, Holy Roman Emperor, king of many places including Germany, Archduke of Austria, etc, etc, started the landsknechte. This was originally a mercenary regiment consisting largely of German pikemen. Emperor Maximilian hired a German (well, we'd call him a German now, then he was a Swabian) named Georg von Frundsberg to organize the landsknechte; he, in turned, hired Swiss mercenaries (mostly officers) to train the landsknechte. This is where the Holbein dagger (and katzbalger and kriegmesser) appeared in German military history.
The landsknechte were early adopters of firearms to supplement and support their pike men, something many other armies and mercenary regiments were slower to do. Particularly in later years, the landsknechte were also almost what we'd today consider to be a "mixed multinational force."
The National Socialist party co-opted a lot of earlier Germanic history and folklore to try to support the legitimacy of the Third Reich. Katzbalgers and kreigmessers were inconveniently large, but that iconic dagger was much easier for people to carry and display, and at least subconsciously signal that the bearer was a soldier. This was done in other areas as well: if you look at the silhouette of some of the uniform designs (not just military--everyone and their dog had a uniform in Nazi Germany, and many groups such as the postal service even had special rifles and bayonets!), you can see similarities to "Almain rivet" (a type of armor worn by the landsknechte at one point). The mixed-nationality aspect of the landsknechte was mentioned a couple times in defense of the decision to add troops of other nationalities to the Heer and Waffen-SS.
During WWII, the Holbein-pattern dagger was never really intended to be a combat weapon; it was a badge of office or membership. It did get used in combat at times: the fighting near the end in Stalingrad comes to mind, as well as a couple of instances during pseudo-surrenders near the end of the war. By all accounts it was an effective weapon.
A friend of mine was a Kripo--Kriminalpolizei (police detective)--during and after the war. He's mentioned investigating a couple of murders where one of these daggers was used. His thoughts are that the grip lock's the user's hand in place, so it didn't slip over the guard in stabbing, or slip from the hand when the user attempted to withdraw the knife from victim. The grip shape forced the user to rely on power in the stroke, rather than finesse. As a result, what he saw in murder victims was multiple deep stab wounds, and tremendous loss of blood.
While the daggers didn't get much actual use, and were largely symbolic, when put to their original use they seem to have been just as effective as the original Holbein daggers.