advantage :share your point of views with others ,personal,technical,professional and soso..,at the same time, you can gain a lot of other's valuable opinions,broad your view
disadcantage: if you are not good at expression, it will cause a lot misunderstands..
Advantage: There are countless advantages.
Disadvantage: Not really a disadvantage, but don't start a personal blog unless you can keep it updated frequently.
not quite you have to write something that is interested to others but of course if you treat your blog just like a personal diary and don't want anyone else reading it that's ok.
But if you want someone will read then you have to find out what most people are interested and what you are interested have in common.
eg. if you like playing video , online games, what other people will be interested in reading?
do a research on forum so that you come up with some ideas