14 Kempo
Grandmaster
One can learn something without a partner and one should practice when there is no partner available. However, it's not as good, and you can only get so far that way. I have personally memorized many many techniques from watching them on video etc. only to find out that that was only about 25% of truly learning the technique. Timing, distance, precision are all things that require a live partner to perfect. In addition, you also need expert guidance to tell you what you're doing incorrectly and how to fix it. So, forms may have some value, but they are not the ideal training device IMO. I think their time is largely past.
I guess I have trouble communicating in writing, I was agreeing with that thought ... just bringing other thoughts to the table. I, in no way, train strictly on my own. I am one that tears down all techniques that I have and finds what works for me against all different sized opponents of different strengths and weaknesses. One thing is true throughout the years, it takes an open mind to learn.