News Courtesy of Yoast.com:
Can Google deal with Lazy Load?
“Yes, it can. It renders the page, it waits a bit and it scrolls down the page a bit to generate all the events that it needs to generate to make sure that it has loaded the entire page.
So yes, it can deal with that. You’re very fine using something like that lazy load image function. Google actually has code itself as well, in which it promotes the lazy loading of images because it really enhances people’s experience because pages get faster using lazy load. So, by all means, do use it. Use it well. Good luck!”
Ryan’s Take 
Website speed is not only important for your visitors, but for Google too. How long it takes Google for a page to render will factor into the SEO of that page. It might not be the #1 ranking factor, but it is something you want to pay attention to for sure.
Lazy loading is one way to speed up loading by only rendering assets within view. There are several plugins available for free on WordPress to accomplish this. It’s not just images that can be targeted. Other assets such as iframes can be delayed in rendering which could have quite an impact if you have many youtube embeds. It’s also not uncommon to see premium themes these days incorporate lazy loading directly.
It’s definitely a good thing that Googlebot is sophisticated enough to wait and scroll through a page before indexing. Think about all that content that might be missed if that wasn’t the case. Depending on how many assets are on a page, that could mean the difference between a high ranking position or off of page 1 in the search results.
Now if your website uses one of those infinity scroll features where news and blogs posts load endlessly, you should expect Googlebot to give up at some point. I’ve always hated websites that use that feature. Mostly because I’m looking for a comment section and the page just keeps going and going. I think pages, even categories should have a beginning, middle, and end. Search results should focus on a single topic or related topics within a page. Not a library’s worth of mixed content.
Despite my gripes with infinity scrolling, lazy loading should be something you implement sitewide. There really is no downside other than some issues that may occur when doing CSS and JS minification (I’ve had problems with the delayed rendering of images long after the asset is within viewport). a3 lazy load is one such plugin that is easy to set up and can help improve speed dramatically. Give it a shot or try some other free plugins and test the results for yourself!
