What is the difference between Annotation Driven and Global extensions in Spock

I'm trying to learn about writing extensions in Spock testing framework. I've come across 2 different types of extensions:

• Annotation Driven (like @Ignore, etc)
• Global Extension (like for integrating spring framework inside the test)

So my question is: What is the difference between them? When should I prefer one type of extensions over another for my custom extensions?

Thanks