Not only will Google penalise your website if it's too slow to load & too heavy to download, but humans will also race to the exit button if your website is taking too long to load - 3 seconds, to be precise.
Why? Because people are time poor and want instant access to your content - they're not patient when it comes to slow websites and Google aren't either.
So how do you know/how can you avoid this Google penalty and keep your website users on your site?
Here are the 3 main culprits of a slow website and how you can avoid them:
1) Large Image Sizes
Large image file sizes take a lot of time to download every time someone lands on your page. If your website is image heavy, meaning you have a lot of images on there, and ecommerce sites tends to have a lot of images for products, then every time some one lands on your website your server has to download every single one of those images.
If you have hundreds, thousands or hundreds of thousands of people are trying to access your website at the same time, that's a lot of work your website has to do to quickly download each image for each person on your site. If your server isn't up to the task? This can lead to your website crashing or not performing well enough for people to stick around.
And they won't.
WHAT YOU CAN DO
REDUCE IMAGE FILE SIZES - There's 2 ways you can do this:
A) Reduce your file sizes before uploading using one of the following websites - birme.net, pilxlr.com or tinypng.com or install a compressing plugin such as smush or short pixel image optimiser.
B) Remove old or irrelevant content that no longer serves a purpose or is expired
More is not more - if you keep adding content to your website but don't remove any that no longer serve a purpose but you can't be bothered removing it, this causes your server to download enormous amounts of content every time someone uses your website.
This then slows down your website which affects your SEO.
C) Disable, remove or uninstall any plugins or apps that your site is no longer using/needs but are still installed on your site
Plugins and apps can greatly enhance your websites functionality and user-experience, but add too many plugins/apps that don't really serve a purpose or by adding too many of them, can cause your plugins/apps to not work cohesively, resulting in a slow loading website and poor user-experience.
HOW CAN YOU TEST YOUR SITE SPEED?
Here's some tried and tested tools
Test your site before and after you make the above changes to your website so that you can accurately measure your site speed to see the huge difference it can make.