Divorce is rarely easy or pleasant. In most cases, trying to get divorced without an attorney is harder or has a worse outcome. Lawyers can be expensive, but not having one when you need one is potentially FAR more expensive.
Here's a brief answer to the headline question.
When You Need a Divorce Lawyer:
When you have kids. Some of the worst post-divorce headaches come from disputes over the children. Child support needs to be calculated correctly and ordered precisely so that the obligation is clear and enforceable. Visitation/possession periods need to be clear and specific. General language won't be enforceable and vague language will lead to disputes.
When one spouse is domineering. That can be physically, emotionally, or financially. Where one spouse can demand and get whatever he or she wants, the other spouse needs a lawyer to help equalize the power in the negotiations.
When there are assets or liabilities. Normally, there will be assets and liabilities that have to be divided between the parties. The division is not automatically 50-50. It can significantly favor one party over the other if there is a big difference in income or income earning potential, or if a party has health issues, or if any of a number of other factors exist. Plus, some assets are overlooked if the parties don't have legal experience or understand how the law applies to their situation.
When You Don't Need a Divorce Lawyer:
When you have a very short marriage.
When there are no assets, liabilities or children.
Those circumstances are rare in divorce cases. Usually, people stay together long enough to acquire things or children before deciding to pull the plug.
The bottom line is that you almost always need a divorce lawyer, if you want to get things done right.
The answer to the title question is — Yes!