Why is wound separation common during breast reduction recovery and how can it be prevented?

The "T" point is an area common for delayed healing. It is a vascular water shed (i.e. relatively diminished blood supply where 3 flaps meet) under high tension.
Patients will typically exhibit some degree of dehiscence (separation) and epidermolysis (sloughing of the upper layers of skin). With some local wound care, these will typically heal secondarily without further intervention.
With regards to your specific question, preventing wounds is a function pre-, intra- and post op factors. Healthy non-smoking candidates who have reached a healthy stable weight (preferably with a BMI < 30) will have reduced risk of complications. Intra-op careful dissection and management of tension is important. Finally, incisional care and support plays a role as well.The best advice is to closely follow the recommendations of your surgeon and be patient as these wounds may take several weeks to resolved entirely.
As always, discuss your concerns with a board certified plastic surgeon (ABPS)
Donovan Rosas MD
Board Certified by the American Board of Plastic Surgery
Member: American Society for Aesthetic Plastic Surgery, American Society of Plastic Surgeons
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Separation at the inverted T zone in breast reduction is a very common occurrence.  The good news here is that even a separation of 1 to 1.5 cm will likely heal and contract very well to produce a nice thin scar.  Just keep it dry and remove the tape. If there is a great deal of wound separation, this may still heal well,  but a revision may be needed in the future. Antibiotics are not needed unless there are signs of infection. Follow up with your PS to discuss your concerns.