"Google Sites is a great tool to create and manage a site."
Google has made Google Sites easy to use, offers support for its products and integrates many of those products into a Google Sites website. But, it has its limitations and may not be a good choice for all websites. Be sure it is right for your website before creating your website and that you are ready for website ownership.
Time. It takes time to learn how to build, update, manage and trouble shoot problems and a commitment to continual learning.
Google Sites tries to balance ease of use and features.This means that websites are easier to manage because there are less features offered but it also means that design and scripting is limited.
Google Sites are best suited to sites with little scripting, simple design and easy management. Google Sites has limited CSS, limited HTML use, no FTP and limited use of scripts (must be in gadgets).
While elaborate websites can be built using Google Sites, it is not recommended for most owners. Google Sites was created to build wiki like websites.
Anything more elaborate requires customization that is beyond the average Google Sites user's knowledge and skills to maintain and takes more time to manage, requires training or an experienced webmaster.
When using Google Sites, simpler is better.