Kid webmasters that want to enter the world of "WWW" by utilizing some freely available resources should definitely go on. But I want them to have an early preview of problems they may face if proceeding with a free web host.
Since free stuffs attract everyone, needy people go there. On the other hand, spammers treat this as a gift to set up a number of non sense sites with no original content. Such contribution to the web has been leading to a bad user experience.
Search engines when evaluate such a site for its ranking, they do check its contents and flag it to protect searchers from exposure to such sites in natural search results. If a good figure comes out of those sites from same host, there stands a great chance of removing the entire host from search result pages.
Kaspar Szymanski of Google Search Quality Team explains,
If a free hosting service begins to show patterns of spam, we make a strong effort to be granular and tackle only spammy pages or sites. However, in some cases, when the spammers have pretty much taken over the free web hosting service or a large fraction of the service, we may be forced to take more decisive steps to protect our users and remove the entire free web hosting service from our search results.
Even free hosting services claim for 99.9% uptime, but hardly provides. If the server goes down, it can take ample time to recover. Admins would not be prompt to troubleshoot the matter for which they are not being paid. This downtime can be devastating and results in traffic loss and thus the profit loss. You can lose a lot of credibility in just a few days. This will also pull down your SEO reputation.
Another thing you are not going to get is the speed, which matters a lot for the web. Generally free web hosts has a much slower response time than the paid one. This slows down the site connecting time and page loading time thereby indicating another weak signal in search ranking.
Not all, but nearly every free web hosting services force ad on the hosted pages. You have no control on what would be displayed in those boxes. Sometimes even malicious links can be there. No matter what's the case, you are helpless to prevent those backlinks from every page of your site. Search engine doesn't have sympathy for sites with such massive backlinks. This may lead to removal of your site from search index or at least will demote it.
There are some other limitations imposed on free accounts like file size, hotlinking, ftp and core language features, etc. If you are not in a position to buy paid hosting, start with a free but reputed one. Choose platforms like Blogspot or Wordpress if they are suitable for your need. And then move to your own domain when you are ready.