For Karate beginners it is important to attend classes of one session in a week, as the learning process progresses then you can surely increase the number of weekly sessions. If you ask me I myself would advise those who are new to karate to make the schedule of getting a karate session in a week and they should carry on this routine for almost first 3 to 6 months, and when this is done then they can start taking 2 sessions on weekly basis. There are lots of tricks and techniques for you to learn and practicing them again and again is the ideal way to master those tactics. If you have been acquiring the training of karate in an institute since the last six months but still you are taking only a single session in a week then it means your learning process is slow either you are not picking the tricks timely or you are not practicing them regularly. This would be definitely a big negative point for you as you may need to put a lot of effort to keep up with your class mates and it may also result in making you disillusioned.
My point for the beginners is that if they keep on getting only a session in a week for several months then their progress rate would be quite slow as compared to the other guys and this will put them far behind the other fellows who are quick in learning and progressing and this may lead to hopelessness in them and it is possible that a time may come when they suddenly decide to quit their training without acquiring much knowledge about different techniques of karate. Therefore the idea is to practice different techniques taught at the training institute at regular basis this will really help you to progress quickly and positively.
It has been seen that many learners of karate start their training with the schedule of one training session weekly and after some time they are still having only one session in a week and then a few months later they observe that they are still there from where they had started. I mean that they find no or very little progress in their karate training so this creates a sense of desperation in their mind and after some time they come to their trainer and say that they are not eligible for karate course and wish to quit it immediately. So if you are a beginner and wish to learn quickly then you should increase the number of weekly sessions timely.