Action hooks and filters are very useful in WordPress. They allow you to “hook" a custom function to an existing function and modify WordPress functionality without editing core files. Here are 10 practical examples of WordPress hooks and filters.
Prevent Automatic Image Compression
By default, WordPress compresses jpg images when you upload them onto your blog. This is useful because it saves bandwidth and loading time, but sometimes you may prefer to have full quality images (for example, if you’re a photographer using WordPress to showcase your work).