If you are applying for a merchant account this is a common requirement of the merchant account provider as this helps them to understand your business model and determine the risk they will be exposed to (e.g. chargebacks). Basically, the more customer friendly they are the less risk they are exposed to.
Privacy policies are good to have as some users, can't quantify how many unfortunately, will at the very least check to see if you have one and some do actually read it. If they don't know what your policies are they may not use your site at all. Additionally, if your website becomes popular ad famous you may catch some flak for not stating your policy at all.
Terms of service are a legal aid to you in case someone abuses your website in some way. It may give you legal recourse should it be necessary but that will vary by country (and state in the US) so you should always consult a lawyer to make sure yours is enforceable.
In some cases, like for example Affiliate Marketing, it is required by law in the USA to disclose such information on your website.
As this article on the Washington Post explains.
To be legally enforceable, they should have been formalized as 2-sided contracts.
Even in this case, of contract formalization between sides, any contract is made null by omnipresent in ToSes illegal claims infringing any laws like reservations (and common use of) of the right of unilateral retroactive (and without any notice!) of an agreement.
Read, for example: