If you are planning on having a website, then you need a webhost. Just because you have a domain name doesn't automatically mean that your site will be up on the web and visible to the rest of the world. You have to have that domain name hosted on a server in order for it to officially be a website.
That's where having a webhost comes into the picture. There are hosting companies out there that provide this necessary service so you don't have to worry about the technical aspect of setting up a server, DNS, etc.
These companies handle the technical side of things to make your life easier. The only challenge you'll face is finding the right one amongst the thousands of hosting companies that are available. And one thing that is for sure is that many of them are not good at all.
You have to make sure you choose the webhost that is right for your needs, whether it be for personal use or business use. Either way, you can't just choose any old host.
Some things you will want to consider when selecting a web- host is if they provide 24 hour emergency customer service, the amount of bandwidth they give you, how many sites you can host on one account, etc. For starters, if they don't offer 24 hour emergency service and you are planning on running a business online, I wouldn't recommend you use that particular company.
Just make sure you do your research before making your selection. Join some discussion forums with people that are in a similar niche or area of interest and pick their brains about this. There are only a few good hosts out there worth using. If you have your site hosted already, I would look into whether or not they are a good company just in case you just picked them just for the sake of picking them.
In conclusion, choose your hosting company wisely as they will be an integral part of your website as long as you use them.