These statements "Opinions are my own and not the views of my employer" serve several purposes that make them not useless.
First, they state a fact - as a reader, I am told that this is not the opinion of the company but the private opinion of someone who happens to be an employee. That's useful information for me, knowing that the company will not be held to any promises this employee made, for example.
Second, it protects the company to some degree. With this statement, nobody can claim that the company is responsible for anything posted.
Third, this protects the employee to some degree. Since posts with such a disclaimer are less likely to cause legal problems for the company, the company is less likely to hold the employee responsible for causing these problems.
Fourth, many companies have a policy that employees should include such a disclaimer, at least if they say anything related to the company. So posting without the disclaimer might be enough to cause trouble with his company for the employee.
Of course, this is not 100% protection. The company won't like it if you say negative things about them.