It is relative. The most important factor to label somebody has low blood pressure is to know his baseline . If somebody is having blood pressure of say 80/50 mmhg for years and does not have any symptom at all . This should not be considered necessarily a bad idea . On the other hand if a person who had blood pressure of 140 /90 came to you with blood pressure of 80/60 , it should be cause for conmen.
Not necessarily. In general people who have low blood pressure live longer. However, if it is low for some bad reason, such as bleeding or infection, then it is not a good thing and could be dangerous. So it depends on the cause of the low blood pressure.