If you are self employed and so have a schedule C you must take all deductions from your self employment income. That is to prevent tax payers from manipulating the earned income credit.
You don't need to take every deduction, but why wouldn't you? If you are itemizing and have more deductions than the standard deduction, then you would record those deductions. If you are not itemizing and are taking the standard deduction, there is no need to record your medical expenses, etc on the tax form. It's not clear whether you are asking about including the deductions on the tax form even if you are not planning to use them, or whether you just don't want to include them for some reason (and possibly pay more tax than you need to)