One thing I don't agree with is that students always have to go off and start their own schools. That always seems to come up in Aikido, moreso than any other martial art. There is always this push to start your own school, start your own school! No thank you, I just want to train please. I don't mind helping out, even teaching and running a class here and there, but don't act like it is a forgone conclusion that I desire to have my own dojo.
Many of the Shihans have pointed out to me that by the time a person is at Sandan, they should have developed their own "style" of Aikido. To do so requires that the person either leave the dojo so that they can practice their own style more easily and consistently without disrupting the consistency of Aikido training in their old dojo or that the dojo have separate classes for each of the instructors who do their own thing. It is not only impolite but also very confusing for students to have several different styles and ways of doing things during one class and the lower rank students are trying to emulate one style when there are several different styles working out on the same mat.
It is inevitable that in open seminars, that there will be several different styles all practicing the same technique differently, but even there, the people on the mat should be trying to do things the way the person instructing the seminar is doing them. Several times, I have been sent by a Shihan to either talk with or do something about a senior rank that was doing things differently in a seminar. The seminar is there to allow you to learn something different, not practice your own thing your own way. This becomes very difficult if the person I have to talk to is of a higher rank than me. But then, that is my job as a Shidoin.
Getting back to the quote, if you find that as a senior rank, you are starting to do things differently from the Sensei, it is time for you to leave rather than disrupt class. Everyone has different bodies and different ideas about Aikido. This is natural. So it is natural to develop different Aikido. There is nothing wrong with this and it is the way of creating the wonderful diversity of Aikido that we find on this website. But, in the dojo, during the Sensei's teaching time, everyone should be trying to do things in the same way. This is the responsibility of the Sempai to their Kohai to keep them from becoming confused. It is not about desire to start your own dojo or not. It is about maintaining good etiquette in the dojo and training correctly and wanting to train to the best of your abilities.
Furthermore, it is the responsibility of the Sempai to help the old dojo grow by starting new dojos with affiliations to the old one. A dojo can only grow so large. It is limited in space and time for practice. The only way for it to grow quickly and without crowding is to develop a new dojo. That is why all social animals have groups that separate from the main colony or hive to develop their own. It is the way of nature to protect the balance of resources to population while still allowing the herd, colony, hive, or dojo to grow and prosper.