One is that you can't have speaker notes integrated in the presentation the same way you can with PP or reveal.js.
The other one is that it doesn't scale. You export the slides in one display ratio and it stays like that. Most web presentation formats will adjust to whatever your display is doing.
I often have complex animations and embedded video that will not survive the PDF export, and am sending presentations to people who can't just be asked to install libreoffice.
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If you're worried about portability, you can export as a PDF. You could also use LibreOffice, which is cross-platform.
PDF has two problems for me:
One is that you can't have speaker notes integrated in the presentation the same way you can with PP or reveal.js.
The other one is that it doesn't scale. You export the slides in one display ratio and it stays like that. Most web presentation formats will adjust to whatever your display is doing.
I often have complex animations and embedded video that will not survive the PDF export, and am sending presentations to people who can't just be asked to install libreoffice.