I ran a quick audit on a handful of small business sites a while back, and the pattern was nearly identical every single time: a homepage with maybe 200 KB of actual HTML, CSS, and text, sitting underneath four to six megabytes of images. Nothing fancy going on with those images either — they just hadn't been touched since someone dragged them straight off a phone.
Page speed isn't just a vanity number. Search engines factor loading time into ranking, and people bounce noticeably faster once a page takes more than a couple of seconds to become usable, especially on a mobile connection. If your hero image alone is 3 MB, that's often the single biggest thing standing between a visitor and the rest of your page.
What usually causes it
Uploading camera-resolution photos directly is the big one. A photo shot at 4000px wide, displayed inside an 800px container, is burning through roughly 25 times the pixels it actually needs. Using PNG for photographic content out of habit is another, when JPEG or WebP would do the exact same visual job at a fraction of the size. And sometimes there's just no compression at all — straight from camera or design tool into the CMS, quality left at whatever the default happened to be.
A realistic before-and-after: a typical product photo, 3.5 MB fresh off a modern phone camera at 4032×3024. Resized to a sensible 1600px wide and exported as JPEG around 75% quality, that same photo usually lands somewhere between 150–250 KB. A 90%+ cut, and the difference is genuinely hard to spot at normal viewing size.
Nobody has ever once complained that a website loaded too fast.
A workflow that actually sticks
Decide the largest size the image will ever display at on your site (check your theme or design file if you're unsure). Resize to roughly that width — there's rarely a reason to go past 2000px for even a full-width hero image. Compress to JPEG or WebP, aiming for the smallest file size that still looks clean at that display size. Repeat before it goes into the CMS, not after visitors start complaining about load times.
Don't forget the small stuff either. Thumbnails, avatars, and icons are easy to overlook because they're visually tiny, but a page with forty 200 KB thumbnails adds up to more total weight than one big hero image sitting by itself. Same resize-then-compress approach applies at any size on the page.
If you're doing this one image at a time, ImgReduce's file-size mode lets you set a target like 150 KB and it finds the best quality that fits, no slider-guessing required.