Istvan is absolutely correct. Don't fall into the trap of adding random, completely unnecessary plugins to your blog simply because so-and-so says it's "good" or because you've seen it on one of those 10 Best Wordpress Plugins lists.

Plugins are often voracious consumers of resources and slow blogs down.

First, discover an absolute need for a plugin (one that cannot be achieved by a few simple edits or tweaks) and only then go hunting for an appropriate plugin to accommodate that need.