The five pound weight is a great start for beginners. It is a low weight that anyone can pick up.
The ten pound weight is a next step from the five pound. This is a good weight for beginners that have spent a week or two working out and also good for drop sets for the more experienced lifter.
The twenty-five pound weight is the first step into some serious weights it is over twice the weight of the previous weight and is a road block for quite a few of beginners. This weight is used well as a target for beginners to weight lifting.
The thirty-five pound weight is a good middle ground for the twenty-five and forty-five pound plates and show that you are on your way to greater lifting heights. This is a good weight to get used to lifting technique for the heavy weight so you won't injure your self later on.
The forty-five weight is the weight that is one of the biggest acheivments for weight lifting and aiming for more of this weight is always a good goal to have when lifting.