Why the sizes differ at all
Platforms store a square and then apply their own mask, and they each picked a different storage size years ago for reasons that no longer matter. What matters is the consequence: upload something smaller than the stored size and it will be scaled up and look soft; upload something enormously larger and it will be re-compressed by their encoder rather than yours, usually more aggressively than you would have chosen.
Matching the target size exactly means the only compression applied is the one you controlled. It is a small difference on a good photograph and a very visible one on a photograph that was already marginal.
Composition for a circle
A circle inscribed in a square keeps about 79% of its area. Everything outside that — the four corners — is gone, and it is gone in a way that draws the eye to whatever is nearest the edge. Backgrounds with strong diagonal lines, or another person's shoulder at the corner, look far worse in a circle than in the rectangle you cropped.
Practical rules that survive the mask: put the face slightly above the geometric centre, because the eyes read as the subject rather than the chin. Leave a little space above the head but not much. Prefer a plain or defocused background — at 32 pixels, a busy background and a face are the same thing. And if you are cutting off the top of the head slightly, that is fine; cutting off the chin is not.
Banners are a different problem
Cover photos and channel art fail differently: they are cropped by aspect ratio depending on the device, so the same banner shows a wide slice on a desktop and a narrow one on a phone. Anything important has to live in the region that survives both. Cover Photo Maker draws those safe zones over your image so you can see which part is guaranteed to be visible.
Before you upload a photo of yourself anywhere
Photographs taken on a phone commonly carry the exact coordinates where they were taken, the time, and the device. A profile picture is one of the most widely shared files a person owns. Most large platforms strip that metadata on upload, but "most" is doing real work in that sentence, and smaller sites frequently do not.
Checking takes a moment with Check Photo Metadata, and re-exporting the picture — which is what the maker does anyway — drops the metadata as a matter of course.