The Shutter Speed simply determines how long the sensor is exposed to light. Common is to use shutter speeds faster than or equal to 1/60 sec to make sure that slight movements of subjects and maybe also of the camera are more or less frozen. In general this works fine. However,
- if the lens becomes too long it is best to take a shutter speed 1/x sec, where x is the length of the lens;
- if due to low lightening the shutter speed becomes too long (less than 1/30 sec) it is best to increase the ISO;
- if the subject moves fast and is close by don’t underestimate the required shutter speed to freeze the subject;
- when using flash it is possible to use a slower shutter speed (for example 1/30 sec) to catch some of the ambient light without blurring the subject.
However, freezing the subject might not be the goal. There are many examples where slower shutter speeds better grasp what we experience: lights of moving cars in the dark, waves of the ocean, waterfalls etc. There is an almost unlimited number of possibilities to use slow shutter speed. Crafts and Vision has a nice eBook about this, called Slow by Andrew Gibson. In this case it is a good idea to use a tripod to avoid movements of the camera. Have fun with experimenting with slow shutter speeds.