Why you'd want a static image from an animated file
GIFs get used constantly for both animated reactions and simple static graphics, but plenty of places you'd want to use that image don't accept animation at all — a forum avatar slot, a blog post thumbnail, a static preview image, a print layout. In every one of those cases, what you actually need is a single frame captured as a normal, non-animated image file.
PNG is the natural target for that, for one specific reason that matters more than it might seem: it preserves whatever transparency the GIF had.
Why PNG and not JPG for this
A GIF with a transparent background — common for logos, stickers, and simple graphics — needs an output format that can represent that transparency, and PNG can. JPG has no transparency support at all, so converting a transparent GIF to JPG would force a solid background color to fill in where the transparency used to be, which is rarely what you want and can look like an outright bug if you weren't expecting it.
PNG also generally handles the kind of simple, flat-color graphics GIFs tend to contain very well, without introducing the compression artifacts JPG can add to sharp edges and text.
Which frame you actually get from an animated GIF
This is worth knowing upfront: converting an animated GIF captures the first frame only, not a frame you pick or the "best" one. This is a direct consequence of how browsers render GIFs onto a canvas — at any given moment, only the currently displayed frame exists to capture, and that's the first frame at the point the image loads.
For a static (non-animated) GIF, this distinction doesn't matter at all — there's only one frame, and the whole image comes through as expected. It only becomes relevant when the source file is genuinely animated and you had a specific later frame in mind.
When you need more than just the first frame
If you actually need to pull out several specific frames from an animation — not just the opening one — that's a different job requiring a dedicated GIF frame-splitting tool with its own frame-by-frame decoder, rather than a simple GIF-to-PNG converter. Know which one you need before you start: a single-frame conversion is fast and simple for the common case, but it won't substitute for full frame extraction if that's genuinely what the task calls for.