When working with raster images (pixel-based) it is important to understand that scaling an image in programs, such as Word, Powerpoint, InDesign, or Dreamweaver, does not actually resize the image, but rather stretches images larger or scales them smaller. When scaling, the resolution is not adjusted to best suit the new size, rather the pixels are stretched and can appear pixelated.
The most common side effect of scaling an image larger than its original dimensions is that the image may appear to be very fuzzy or pixelated. Scaling images smaller than the original dimensions does not affect quality as much, but can have other side effects. For example, if you upload a very large image to a website and scale it down to a smaller size, the website still must load the full size version of that image and could cause the web page to load more slowly.
3 March 2021: Maximum file upload size updated to 250 GB. 16 September 2020: Updated info about OneNote notebooks to clarify that the 2GB file size limit applies to SharePoint as well as OneDrive. 31 August 2020: Updated the invalid or blocked file types guidance about.PST files when Known Folder Move is turned on.