To start the juices flowing for mission builders...a quick collation of combat units stationed on Canon's Kharkov map region (excluding recon units, a lot of recon Ju88, Bf110 and Fw189 were also stationed in the area)
1942
III/JG77 Bf109F
stab/JG3 Bf109F/G converting
I/JG3 Bf109F
stab/JG52 Bf109F
II/JG52 Bf109F
III/JG52 Bf109F
I/JG53 Bf109G
stab/ZG1 Bf110
I/ZG1 Bf110
II/ZG1 Bf110
III/ZG1 Bf109E
stab/ZG2 Bf110
7./ZG2 Bf109G
II/StG1 Ju87D
stab/StG77 Ju87B/R, Bf110 converting
I/StG77 Ju87B/R, Ju87D converting
II/StG77 Ju87B/R
III/StG77 Ju87B/R
stab/KG27 He111H
I/KG27 He111H
III/KG27 He111H
IV/KG27 He111H
I/KG51 Ju88A
III/KG51 Ju88A
I/KG55 He111H
I/KG76 Ju88A
1943
II/JG3 Bf109G
I/JG52 Bf109G
III/JG52 Bf109G
I/ZG1 Bf110
stab/StG2 Ju87D
I/StG2 Ju87D
II/StG2 Ju87D
III/StG2 Ju87D
10.(pz)/StG2 Ju87G
stab/StG77 Ju88A
I/StG77 Ju87D
II/StG77 Ju87D
stab/KG27 He111H
I/KG27 He111H
II/KG27 He111H
III/KG27 He111H
IV/KG27 He111H
14.(Eis)/KG27 He111H
II/KG51 Ju88A
II/KG55 He111H
III/KG55 He111H
14.(Eis)/KG55 Ju88C
I/KG100 He111H
Obviously Kharkov region is a major combat arena and staging platform. It was one of the USSR's primary industrial centres, then became a major German base a lot like Smolensk to the north and a transportation network for German supplies, especially for shuffling Luftwaffenkommando Öst units around between say, Rostov or Majkop one month and Orel or V'yazma another. Without Kharkov Luftwaffe mobility across the Front would be cut to pieces and the absence of Luftflotte 2 would probably have been a war losing proposition. With Kharkov secure virtually the entire southern Front could be kept zipped up, it is no coincidence that following Stalingrad Kharkov was the first Soviet target and following that, it was Manstein's very first and most important strategic re-offensive. Retaking it in 1943 stabilised the Front and could've allowed an orderly retreat to entrenched positions in the Ukraine but alas, Hitler was a moron.