Eguchi et al1 show that real blood pressure differences between right and left arms are rare, but when present, indicate arterial obstruction on the side where the blood pressure is lower. They note that it is still recommended that blood pressure be recorded bilaterally on the first visit to detect those rare individuals with arterial obstruction in the upper extremity circulation.
Hege JS. Palpable Pulse Delay in Subclavian Steal. Arch Intern Med. 2007;167(22):2530. doi:10.1001/archinte.167.22.2530-a