I'm a lawyer, and I think a lot of legal services don't provide great value for the consumer. Wills, on the other hand, are a veritable bargain (our office charges $650 for a set of two wills, powers of attorney, and health care directives (sometimes called living wills)).
I've handled several litigation files where people have tried to save money by doing their wills themselves. They ended up costing their beneficiaries thousands, to save a couple of hundred dollars. One woman- a professional- typed up her own will using a kit. She only got one signature on the will- a neighbour who was already quite old when he witnessed the will. That automatically meant that the will was not a formal legal will (which requires two signatures in my province), so that at a minimum, an expensive and time-consuming court application would have been required to administer the will, and the distribution of assets would be delayed for months.
It was worse, however. When the woman died, years later, the lone witness had dementia and could not verify that the signature was his or that he witnessed the will. The two sons believed the two daughters had applied undue influence at the time the will was written (the will broke a long-held promise to gift farmland to one of the sons), and the lone witness was of little use to testify to the mother's capacity or undue influence by the daughters. We eventually settled the matter without the need for court, but the total legal bills for both sides consumed about $20,000 of a $200,000 estate.
When I do a will for a client, I am essentially providing a formal legal opinion on capacity, one that a court will likely find reliable if the will is disputed down the road. I take detailed notes if your capacity is at all in issue. In my province a will can be challenged on the basis it does not adequately provided for a dependant (which can include an adult child in some circumstances). I therefore take detailed notes about your instructions when someone is left out of a will or receives a lesser share, which can be helpful if that individual ever challenges the will down the road. I talk to you about the possibility of setting up a trust for any beneficiaries that might be under 18 (or 25 at the time of your death). I talk about what will happen if at the time of your death you no longer own the particular home, or car, or antique watch that you want to gift to a specific person. We will usually have one lawyer and an articling student or legal assistant sign as witnesses, which means the witnesses will be easy to find decades down the road when one of the witnesses must swear that they witnessed the signing of the will. We keep a copy of the Will in our fireproof safe, or file it at the courthouse, depending on your preference. We also ask questions to rule out potential problems (like hidden offspring, or complex assets, or contingent gifts).
In the end, the document I draft usually looks superficially similar to a well-done "kit" Will. The work is behind the scenes, and well worth the money, in my opinion.
This post is pretty good evidence of how bad people are at drafting their own wills, unfortunately.