Will image styles be applied when they do not logically apply?
It is all up to the PHP toolkit used to manipulate images. The code that is executed from the image effect is the following one. (See image_scale_and_crop_effect().)

function image_scale_and_crop(stdClass $image, $width, $height) {
  $scale = max($width / $image-&gt;info['width'], $height / $image-&gt;info['height']);
  $x = ($image-&gt;info['width'] * $scale - $width) / 2;
  $y = ($image-&gt;info['height'] * $scale - $height) / 2;

  if (image_resize($image, $image-&gt;info['width'] * $scale, $image-&gt;info['height'] * $scale)) {
    return image_crop($image, $x, $y, $width, $height);
  }
  return FALSE;
}


The IF-statement is only used because image_resize() can return FALSE if the PHP image toolkit doesn't support the operation being executed on the image. The function called from image_size() (image_toolkit_invoke()) is generic, and it doesn't make assumptions about the operations currently enabled from the selected image toolkit.