Generally Google bots crawl when they wanted to. So when you fetch your url it means that you are telling google bots to crawl your site as soon as possible because you have made updates in turn it increases the indexing time of your urls also.
Well said expmrb.
I don't think it directly helps in SEO but if you have updated on site content.....you can use to it index fast.
That's actually the use of fetch as Google Bot, if you made some updates with a website or specific page, you can do the
"Fetch as Google Bot" process to let Google know that there are major updates with the site, and also to make it more possible
for it to be indexed faster.