You should certainly work out with friends. Exercising with a friend comes with an advantage: you’ll be more likely to do it. If not, you will be disappointing someone else by breaking the appointment. This is a form of accountability, and a good way to remember and carry through on your commitment to enhance your fitness and your health.
Also, exercising with a friend can provide distraction and good company for what might otherwise be a more boring task. Not only will this give you a walking partner, but it will also provide you with an opportunity to catch up with each other in a relaxed environment.
Depending on the relationship and relative level of exercise ability of you and your friend, there can also be the benefit of support, encouragement, and even a little healthy competition!