Converting Vector to Raster: What Actually Happens
SVG is a vector format — shapes described mathematically, with no inherent pixel grid — while PNG and JPEG are raster formats, fixed grids of pixel values captured at one specific resolution (see SVG vs PNG for the deeper scalability comparison). Converting SVG to a raster format means rendering the vector math at a chosen output resolution, baking the shapes into a fixed pixel grid at that exact size — a one-way process, since a rasterized image can no longer be scaled back up without the blurring/pixelation that raster formats are inherently subject to.
Choosing the output dimensions matters more here than for most conversions, precisely because that choice is permanent — an SVG rasterized at a small size can't later be exported larger without re-running the conversion from the original vector source at the new target size; the raster output itself has no more detail to reveal beyond what was captured at conversion time.
PNG output preserves any transparency the SVG had; JPEG has no alpha channel at all (see JPEG vs PNG), so an SVG with transparent regions converted to JPEG will have that transparency replaced with a solid background color — worth choosing PNG specifically whenever the source SVG relies on transparency.