The resort fee amount varies by property and location, but the fixed amount is typically charged on a daily basis, so it can set you back quite a lot of money. The majority of resort fees cover perks like free internet services, gym entry and access to the resort pool if there is one.
Resort fees are usually charged to cover amenities like Wi-Fi and gym access, but they're not optional. You have no choice but to pay them even if you choose not to use the amenities they cover.