Very simply a compounding pharmacy as able to create the exact dosage for an individual person - with the dosage ingredients that are most suitable for you.  The medications are made (or compounded) to match the exact prescription you have from your doctor.  And this can be done so that the medication is is the best form for you - perhaps a capsule, suspension, troche, ointment or cream.  You can also be certain that nothing else is in your medication - free of dyes, sugar, or ingredients that may cause you discomfort.