A stepper-motor is often used in projects where robustness is required. The device's simplicity ensures a good chance of it working even in some pretty hostile arenas – for example where dust or sand is present in quantity, or where there is a risk of water ingress into a project. It's also relatively cheap, which means the hobbyist is able to instil some movement and positioning control into his or her project without spending over budget.
There is, though, a problem with the use of the stepper-motor. In fact there are two. One is that the motor itself limits the designed in terms of size – and the other, that there's a torque limitation as well.
Let's attend to the size issue first.
The stepper-motor is essentially a metal gear cog surrounded by electro magnetic coils. The cog is moved by switching different coils on and off in a sequence. Every time the cog moves, it has performed one "step" in its complete sequence – hence the name of the motor.
The more complex the dance you want your cog to be able to perform, the more cogs you need on the wheel. This is also true for positioningaccuracy. If you want to be able to accurately position something, such as a laser pointer, using a stepper-motor cog, you need lots of small teeth rather than four or six big ones.
When you make a big cog tooth walk through a step, its size and weight causes the wheel to run through the optimum point of magnetism and out the other side. The activated magnet then drags the point of the cog back to the pole position, causing a perceptible wobble in the motion of the wheel.