Presumably there is a tax implication too? In the UK this would probably be a benefit-in-kind and taxed say it's market value as income.

Yes. Same in the US. Things like private jet use are applied as income. However, I'm not sure you would have to do so at retail rates. For example, you would have to pay taxes on the cost of the private jet use. The marginal cost of something like running your personal ads on the favebook platform is so low as to probably not be considered "material" by the tax man.

Considering he controls 60% of the company, such controls are meaningless.

The controls would be something agreee to as part of taking the company public or some stage of auditing.

Owning a controlling stake doesn’t mean you can fiddle around with every corporate asset at your whim.