I love my bob, it is one of the best training aids ever IMHO a lot better than a bag, and I have had numerous bags.
I started training on my own many years ago as a supliment to attending my local karate club. I wondered what I would do if I ever had my own school or taught people , then I would only have myself as a motivator, I also wanted to get better at my chosen activity. I found that there are many benefits to training on your own, in my case it meant I could stay in shape when no schools were available, also I can dictate my own pace and train around injuries, I also found that we tend to hold back when we train with people especially if you train with weapons such as in escrima, there is a tendencey to hit the other persons stick rather than focus on hitting the person, now I train full power hits on poor bob with the sticks...also there are some things that require loads of practice to get right such as twirling nunchakus and you can only really get it right by solo practice.
This does not mean of course that you can't learn from other people or even attend karate clubs it's just an extra dimension to your karate.all the masters practice on their own, which is why they are masters and it's also IMHO why you have things like kata, it;s another dimension again to your solo training