What is a plugin?
A plugin is a piece of software that runs on your WordPress website which adds or extends functionality not currently in the core of your WordPress code. Plugins can do everything from stopping spam to creating a fully functional membership site.
As Darren explains, each WordPress plugin you add to your website has an effect on your load time (how fast your website pops up with someone types in your URL). Therefore, you must choose carefully when selecting a plugin, and you must thoroughly investigate each plugin you consider using.
Where do I find plugins?
There are more than 50,000 plugins in the WordPress plugin repository. Each plugin has it’s own page with statistics on how many times it has been downloaded and how active the support forum is.
How do I choose?
Make a note of how many 5 stars reviews there are, as well as how many 1 star reviews. What are the users saying? Are the plugin owners answering questions in a timely manner?
Note the date the plugin was last updated. Is the plugin still being maintained or has it gone stale with no recent updates?
As WordPress evolves, new versions are added. When you are updating to the latest version of WordPress, review the plugins on your site to determine if they remain necessary or useful. Has the functionality you are looking for been integrated into WordPress itself? If so, perhaps you can remove a plugin or two and improve site speed!