Transhuman augmentation offers tremendous potential to military organizations, but augmentation isn't free and good morphs are certainly not cheap. Programs for standard augmentation, once the costs of surgery, downtime, and augment-usage training are factored in to the equation, can quickly become impractically expensive, even for hypercorps. Those augmentations that become standard are those whose benefits best outweigh their costs.
The multitasking augmentation, requiring only a cortical stack and therefore compatible with virtually all morphs, has become one of those standard augmentations. The primary disadvantage is the need for skilled soldiers, as forks have the skills of their originals and the most effective multitaskers will be those who can fill the roles of multiple types of specialists as well as typical soldiering.
The first fork is the most like a traditional soldier. This fork has direct control of the body, shooting, moving, and otherwise doing what a soldier would be expected to do. This fork is the only one with bodily control, and will typically be the only one using its senses as well.
The second fork maintains communications, tacnet, and operational awareness. This fork acts as a voice in the ears of the other two, giving important information, relaying orders, navigating, and keeping an eye on the situation as a whole and updating the others when needed. This fork typically spends its time in a simple VR environment containing tacnet feeds, communications, maps and other important sources of information.
The third fork typically specializes in infosec or bot-jamming, depending on what is needed. In the post-singularity battlefield hacking can be a powerful weapon, in the hands of one's enemies as well as oneself. An infosec specialist fork exploits weaknesses in enemy communications, but their primary task is typically defensive. It is also common for the third fork to be tasked as a bot-jammer, maintaining control of a small group of combat drones. A multitasking soldier who is actively fighting, maintaining situational awareness, and with control of several drones is as effective as a squad.