Should you show excerpts or full posts on your blog's homepage?:

Should you show excerpts or full posts on your blog’s homepage?

I’m an independent Science Fiction author who has recently set up a blog to promote myself and my work. I’m going to be talking about writing, publishing but mostly science fiction. The goal is to draw in traffic to my blog, build up a bit of an audience and hopefully convert them into book sales.

Here’s my concern. I like my blog’s theme, particularly how it shows excerpts on the homepage with a featured picture. But I’m worried that this stops people from actually reading my content, since they have to click through to read and then click back to read more posts. Is it better to have the full posts displayed so people can just read through? I’ve also heard that excerpts is better for google rankings, as it flags up less as duplicate content, but is this really an advantage if nobody is reading?

What would you say are the advantages and disadvantages of each option?