Others do not think this is needed when metal plating is used along with bone graft material. There haven't been enough studies done to fully answer the question.
It may be best if the decision is made on an individual basis. Patients who are only having a single-level fusion are less likely to have loosening at the fusion site. They may not need bracing at all.
But patients with reduced or poor bone quality, multi-level fusions, and allografts (donated bone) may need the extra support while fusion takes place.
A recent study from Baylor College of Medicine in Houston, Texas reported on this topic. They found measurable motion within the first two weeks after anterior cervical discectomy and fusion (ACDF). Adjustable titanium plates were used.
They thought the plates would reduce the motion enough to encourage the bone graft to form a bridge. The patients didn't wear a brace of any kind afterwards. This may have resulted in loosening at the bone-to-screw interface.
If you have osteoporosis (decreased bone mass) and multi-level fixation, you may want to consider post-operative bracing for the first week or two. Your surgeon is the best one to make this decision.
The type of injury and quality of bone will determine the selection of implant used. Some implants have greater variability and are more likely to bend or provide too much rigidity at the fusion site.