Yes. Because a lot of our links are to within a page (www.example.com/page1.htm#widgetA) and not specifying the image dimensions causes GUI browsers to jump to the wrong part of the page (they display the correct part, but then scroll as images come along moving the text up). A real issue for sighted readers using a standard GUI browser...
Define "certain movement" and "problems" in reference to "some users".
I'm not referring to Flicker or Strobe effects. Just movement in general on the page. Whether it be images loading in their placeholders, an animated gif, a Flash movie, basically anything that has movement. We're talking a very small percentage of users who may be affected by these.
True. But while that may be the case, at least you are limiting the movement by ensuring that space is reserved for the images. If they have that problem, they will most likely surf with images turned off.