The choice to go with a free web site over a paid service is one that should be considered carefully based on your needs.
Free web sites are generally highly impractical in most cases if you're wanting to set up a database driven web site. If that is your purpose then you'll be hard pressed to find a free web host that will enable that kind of web site for no cost.
If you plan to make a more general, informative style site with plenty of your own free content or you're looking to start an online business (or get your business online) with little cost then a free web site may be practical for you.
No matter what you will be using the site for, if you are just starting out, then a free site is an ideal way to see if you're going to stick with keeping the site updated over the medium to long term. There's no point in spending money only to discover a web site just doesn't suit your purpose, schedule, interest or you just can't be bothered keeping it updated. Nothing lost, nothing gained.
If you're using a free web site for personal use then you'll have many more choices for which web host to go with. If you intend to run a business from your free site then be sure to check that your web host's Terms and Conditions of use permits their free sites to be used for 'commercial' purposes. Many don't. You don't want to find your site suddenly shut down simply because you didn't check.
From a practical point of view free web sites often come with desirable easy to use options. For example Freewebs (www.freewebs.com) is great for people who have no web design experience because you can choose one of their many professionally designed templates. They make it easy to add functionality like guest books, forums, photo albums, shopping carts, payment buttons, subscription boxes and more all without needing to know a scrap of HTML, Java script, PHP etc. They also feature their own online WYSIWYG (What You See Is What You Get) site editor.
On the negative side the majority of free web sites are not actually free. They usually come with the caveat that you can use them free if you're prepared to have advertising banners automatically inserted into your web site pages. Freewebs, for example, will place a Google banner advertisement across the top of every page of your site.
On a personal site the advertising may not be an issue however if you're running a business you may just see competitor advertisements appearing in those banners. Not always but possible.
If you're looking for a free web site host that doesn't place any advertisements on your site then 50webs (www.50webs.com) offers a great advertisement free account. However their service is better suited to people who have their own web design software and know a bit about design. 50webs is great for people who want to completely customize their web site from scratch.
A free web host is less practical when it comes to the address (URL) of your site. If you want a URL people will remember then you'll need to check what the URL of you free web site will be once you create it. Many are long, difficult to remember and usually include the web host's own URL (e.g. www.myfreewebsitehost.com/users/yourwebsite). Not easy to tell your friends or fit on your business card.
The best way to get around this is to pay for your domain name so you can at least have a URL like www.myname.com (much easier to remember). Once you have your domain name you can then point it to your free site. In a practical sense it's not the web site that is the most important aspect of having a web site it's actually the ease with which people can remember how to get to it. That said, you don't want people to have a bad experience on your site otherwise they probably won't come back even if they remember your URL.
Something else you'll need to confront is the amount of traffic your site will receive and bandwidth (the measure of how much data that can be exchanged between your site and it's visitors - usually allocated by the month) it will consume. Does your free web site host put a limit on your sites bandwidth and, if so, what is that limit? Many free sites do limit their bandwidth and offer greater or unlimited bandwidths on their paid services.
For the most part you may not have to worry about bandwidth to begin with however if your site becomes frequently inaccessible due to constant maximizing of bandwidth usage a free site may no longer be practical for you.
In summary a free web site is practical for beginners and/or anyone starting a new web site that doesn't require too many advanced features or want a database driven site.
Most web hosts that offer free sites also offer paid versions with more features. Hence it is possible to stay with your free web site host and graduate to a paid web site as you begin to grow and expand.