Basicaly 5 important ideas are there behind writing a blog:

First : Socialise your Views

Sometimes when you are alone you mind talks to you and give some valuable views, which might not help you but may help others. So it is the good decission to socialise the view.Blog is the only way to do that.

Second : Judge your Personality

Your thoughts,interests always represent your personality. So here you can get the response from society about your thoughts,interests that how the society takes your thoughts, whether they appreceate your thoughts or contadict. Whatever may be but you can judge youself by the comments.

Third : Analyse your thoughts

You have a thought but you want to spread the thought and get the response frrom society about this to know how the society takes your thoughts.Is it same as you think or your thought is not so perfect.Whatever may be you can get to know that how you are thinking and how the society reacts towards your thoughts.You can easily analyse your thoughts and change or convince accordingly.

Fourth : Taking social debates

You can post social debates in a blog which will help you to get the response from society both in support and in contradict which in turn provide you a tons of information for ypur thoughts about that debate.

Fifth : Improving writing skills

Yes according to me this is the perfect way to increase your writing skill. As you know you are going to publish your blog and it should be viewed by tons of people, so you will try to make your writing as clear as possible, as beauty as possible, which inturn helps you to improve your skill gradually.

Apart from these many more skills,benefits we can get just writing a blog.

So writing a blog is a better practice to do and a better way to craete youself along with the society.