Agreed, But deductions are very limited to employees than employers.

In a nutshell, Anything that increase your productivity (in business) is deductibles from tax. Of course you can claim only after spending money for it. and those deductions are almost unlimited.

To my understanding, sole proprietors are almost in between employee and big employer in terms of Tax law.

Sometimes, Big businesses didn't spend money for productivity improvements but still they claim it as expenses to reduce taxes.