Email counselling can be useful if you have a difficult time talking about your feelings. Some people find it a lot easier to write things down. It's also really useful if you want plenty of time to think about what to say, and to think about my responses.
However, there are some downsides and the main one is that it can be easy to miscommunicate or misunderstand the written word. When we talk face-to-face we can hear tone of voice and see facial expressions and body language which help us to understand the other person fully.