What is a widget and why do you want one?
A widget is a chunk of code that you can embed into your website and usually displays a slide show of images, or other arrangements of images you have selected. You get the code from the website offering you the widget. Let's look at a Flickr widget, for example. You upload pictures into your Flickr account. You "tag" them with words that have to do with your pictures, like "Paris vacation" or "birthday party" or "friends." You go to the Tool area in Flickr, and create a badge (some websites call widgets a badge...I know, it's hard to keep up). You tell it you want a badge, or widget, of all the pictures you tagged "paris." Then it will create this small slide show of pictures that pop out at your users, who can then click on it to see all of your wonderful photos.
Here's a free widget from my Flickr account of websites designed by Katie James Pixelated:
You can also use widgets for ecommerce, like if you had a store in Etsy.com, or just for fun with StyleHive. And, if you have affiliate accounts with websites, like Amazon where you make a commission of whatever anyones buys from Amazon once they click on a link from your special Amazon affiliates link (here's a write-up of the Affiliate program from an LWLer), those websites might also offer widgets to you. Amazon rolled out some cool ones, like this slide show that I made just now:
Are there drawbacks to using widgets?
Sometimes setting up the widget can be buggy. Amazon's navigation, at times, is not the easiest, so it's very easy for me to click on the wrong link to get my code, which causes me to lose all of my work. What work? Selecting which books I want to appear in the slide show, for example. That's it. So I just need to re-invest the brain power to remember which books I wanted to add.
Also, you are pulling data from another website, so that can cause your load time to run more slowly, especially if you have many widgets on your site. Like all things, though, companies providing the widgets will improve with time as they invest more in their ability to serve you faster.
And finally, a widget can sometimes not fit very well into your website design. So if you are going to build a website, keep in mind that you want room for these sorts of things. Certain designs, like my blogger template of the moment, look clunky with some widgets. I'm widget-happy, so I will continue to use them until I give blog a major make-over. Come visit if you want to see some more widget examples and ways I've used the widgets.