There are many features available for websites today. Do you need to sell products? Then you will need an e-commerce plugin like WooCommerce. Do you need the ability for users to signup for newsletters and the ability to send out newsletters to your customers? Then you will need your website to be set up to do these things. Some more examples of additional features you may want for your site include: an events calendar, blog, online booking, Google Analytics or Google Maps. All of these are features that require extra time and effort to set up and deciding what you want from the beginning will allow you or your web developer to choose themes that work well with the functionality you require.
For example, a local restaurant needs a website so customers will know where they are at, when they are open and what they have on the menu. This site could be done in a very simple way by creating a few simple pages with static content. They could have a page with their contact info, hours and a map, a static menu page and a home page that tells a little about the restaurant. This is fine for some businesses. This is a short and sweet and CHEAP solution. But, what if the restaurant needs their customers to be able to order food online and they need integration with GrubHub or DoorDash? This is more complicated and will take more time. The restaurant may also have seasonal menus that they would like to display at different times of the year. This could require the use of a menu plugin that allows the restaurant to choose which menu is being displayed right now. The company might also need a team plugin or specialized franchise or branding styles that need to be created to match specific guidelines. These are things that incur more time and more cost.
Before building a website or hiring someone to do it for you, you must decide what you want your website to do. List all the things you want to be able to do with the site. List all the things you want your customers to be able to do with the site. This will help you know what extra bells and whistles you are going to need and how much all of that is going to cost ahead of time you you can plan for it. A great website will pay for itself in the first year or two by driving more customers to your door. Keep this in mind when determining your needs.