PNG became the default for the wrong reason
Plenty of apps and tools default to saving every image as PNG regardless of what's actually in it, simply because PNG is lossless and "safe." That's the right call for a screenshot, a logo, or a graphic with sharp edges and flat colors — but for an actual photograph, PNG's lossless compression means the file is often 5-10x larger than a visually identical JPEG, for zero visible benefit, since a photo doesn't have the hard edges PNG is optimized to preserve perfectly.
The result is a phone gallery or website full of PNG files that are secretly just oversized photos, quietly eating storage and bandwidth for no reason anyone actually needs.
The one PNG feature JPG genuinely can't replicate
Before converting anything, it's worth checking whether your PNG actually uses transparency (an alpha channel) — because JPG has no concept of transparency at all. If your PNG is a logo or graphic with a see-through background meant to sit over other content, converting to JPG will force that transparent area to become a solid color, which usually isn't what you want. A proper conversion tool lets you choose exactly what that fill color should be (white is the safe, common default) rather than leaving it to an unpredictable automatic choice like black.
If your PNG is a straightforward photograph with no transparency at all — which describes most photo-content PNGs — this concern doesn't apply, and converting is close to a pure win.
Why converting screenshots and logos to JPG usually backfires
JPG's lossy compression is tuned for photographic content — smooth gradients, natural textures — and performs noticeably worse on graphics with sharp edges, flat color regions, and text, which is exactly what a screenshot or logo consists of. Converting that kind of image to JPG often produces a result that's both blurrier around edges and, counterintuitively, sometimes not even meaningfully smaller than the original PNG. This is the one case where the PNG-by-default habit was actually correct — keep screenshots, logos, and diagrams as PNG.
Finding the right quality setting without guessing
85-92% quality is a solid default for photo conversions — high enough that compression artifacts stay invisible in normal viewing, low enough to meaningfully shrink the file compared to the source PNG. A good conversion tool shows the exact before-and-after file size as you adjust the slider, so you can see the actual trade-off happening in real time rather than guessing and re-downloading repeatedly to check.
If you're converting many similar photos at once, settle on a quality setting with the first one and reuse it across the batch rather than eyeballing each conversion separately — consistency matters more than squeezing out a marginally better result on any single image.