HubSpot's file manager will automatically resize images on your website to decrease page load time and increase your Google PageSpeed score. If you are seeing any warnings regarding images, check with your designer to see if you are using any background images that are being loaded initially at a large natural size. It may be a good idea to upload those images to HubSpot at a smaller size for use in your designs.
Google mentions that the PageSpeed Insights tool's recommendations are "biased in favor of speed" and that "you need to evaluate the cost of making changes vs. the benefit the rule would have on your page." It is also important to consider the experience of your visitors when making any changes to your website. For more recommendations for improving your page load speed in HubSpot, please see this article. Additionally, if you are interested in improving your load time for your blog on mobile, please see this article about using Accelerated Mobile Pages (AMP) in HubSpot.