While a stockbroker may have an insurance license and an insurance agent may be fluent in mutual fund lingo, these areas are too complicated and change too quickly for anyone to be an expert in both. Think of it this way: If you broke your arm, would you call a veterinarian? While he could probably set your limb, your fur may never grow quite the same way. By acting as a consultant, your financial advisor can help you reach your goals more efficiently and with a lot fewer mistakes than a specialist.
You should be equally careful about what advice you take from investment newsletters. While some provide substantial expert advice, others are worth less than the paper they're written on. Check a writer's track record before "subscribing" to their ideas.