The default screenshot tools on macOS and Windows capture exactly what you can see — the visible viewport. The thing you wanted to capture was usually longer than that: a chat thread, a settings page, a spreadsheet, a code review with twenty comments. So you take screenshot, scroll, take another, scroll, take another, and now you have six images with overlapping content that you have to mentally splice together.
A scrolling screenshot collapses that into one tall image. One file to attach, one file to mark up, one file to send to the person asking “what does the whole thing look like?” You scroll, the tool captures, the result is one PNG.
PrintScreen.ly ships scroll capture on both Mac and Windows, with the same keyboard hotkey, the same editor, and the same save folder pattern. It doesn't need a browser extension — it works on the OS itself, so it captures whatever can scroll: web pages, native apps, file listings, terminal scrollback.