Question

What are potential pros and cons of having such tests done and of referring to DNA sequences when determining a patient’s medical treatment?

Answer 1

I think the cost is the main deterrent. A pro could be discovering certain recessive disorders.
Here is what the human genome project says the potential benefits are:
Molecular Medicine

Improved diagnosis of disease
Earlier detection of genetic predispositions to disease
Rational drug design
Gene therapy and control systems for drugs
Pharmacogenomics "custom drugs"
Technology and resources promoted by the Human Genome Project are starting to have profound impacts on biomedical research and promise to revolutionize the wider spectrum of biological research and clinical medicine. Increasingly detailed genome maps have aided researchers seeking genes associated with dozens of genetic conditions, including myotonic dystrophy, fragile X syndrome, neurofibromatosis types 1 and 2, inherited colon cancer, Alzheimer's disease, and familial breast cancer.
On the horizon is a new era of molecular medicine characterized less by treating symptoms and more by looking to the most fundamental causes of disease. Rapid and more specific diagnostic tests will make possible earlier treatment of countless maladies. Medical researchers also will be able to devise novel therapeutic regimens based on new classes of drugs, immunotherapy techniques, avoidance of environmental conditions that may trigger disease, and possible augmentation or even replacement of defective genes through gene therapy.
http://www.ornl.gov/sci/techresources/Human_Genome/project/benefits.shtml