My two pennies worth...
If you have lots of companies trying to provide goods and services, those with the best quality and price will thrive...capitalism if you like, working.
If you have natural monopolies, such as water, power, rail etc. Handing them over to a private company will usually result in poor service, high prices and the owners reaping high dividends.
A case in point, is water, I have read, since privatisation £72bn has been distributed as dividends and cash buy-backs. I believe no new reservoirs have been built, leakage is still about the same and siht and pollution is put into rivers and seas.
Rail privatisation has lurched from one crisis to another, with the Govt having to take over.
As for power..it certainly doesn't seem to have been managed for the benefit of its customers.