The difference in your bank account balance between paying a property manager 11.67% (10% of gross rents plus 20% lease fee) and managing the property yourself when buying one 20% down rental property (in Northern Colorado) over 40 years is:

If you invest the difference in the stock market and could get 8%, the difference becomes:

If you're saving for a second purchase, it delays when you can buy that second property which further compounds the effect of property management fees on your overall net worth.

And doing the full Nomad investing model, it is pretty significant differences.

I am going to write a whole book about the impact on various investing scenarios.