I was checking my sites page load time. I saw that I could improve it by reducing the size of the images which were getting resized by css. Now I wanted to ask if resizing the images is worth the page load speed? As it takes quite good amount of time to do the resizing so is it strictly recommended for a good website? Thanks in advance.
Yes, it is. Making users download useless extra image data just so the browser can resize the image to less than half the size is bad practice, and it's one of the warning signs of a poorly designed/developed website.
If you want to improve page performance why wouldn't you reduce unnecessary bandwidth usage? That's like asking, "If I want to get better mileage, should I patch the leak in my fuel tank?" Well, of course you should! A leaky gas tank is the exact opposite of what you want to get good gas mileage.
If you're making users download dozens of 800x600 images to view your page, is it really any surprise that the page performance is poor? And at the size the images are being displayed, almost 80% of the transferred data is just useless junk. You may as well have a page that has 10 visible images on it but loads 40 other images that are never seen by the user.
If you're concerned about speed, not only should you resize images but also consider creating CSS sprites to combine multiple background images into a single image using an online tool like SpriteMe or CSS Sprite Generator.