Depends on what we or you are making 🙂 like an image logo for your website or maybe a cool 4K wallpaper size image of any gaming related. For me and it always defaults anyway while opening photoshop that it's 1920x1080 🙂
Doesn't matter how big the white background is, end of the day you can always trim it 🙂
I usually make graphics that are intended for websites, so I make resizable SVGs without thinking so much about the exact size, and then alter the size through CSS later on.