The answer to this question will depend on the preferences and circumstances of each individual.
As your assets grow and your financial picture becomes more complex (with unclear tax implications, and interdependent asset classes), then the answer is more likely to be yes. For those investors with a more modest-size portfolio, it may not be necessary.
Financial modeling tools and market research publications are widely available, and while they are not one-size-fits-all answers, they can serve investors quite well when used wisely. Investors who choose not to consult an advisor must be willing to educate themselves.
Many related questions and concerns are addressed in these Forums and articles, where you will find guidelines to help you decide if a financial advisor is right for you.
Where do I find a Financial Advisor?
How Fast Should My Portfolio Grow?