scroll: This value indicates that the content is clipped to the padding box, but can be scrolled into view (and therefore the box is a scroll container). Furthermore, if the user agent uses a scrolling mechanism that is visible on the screen (such as a scroll bar or a panner), that mechanism should be displayed whether or not any of its content is clipped. This avoids any problem with scrollbars appearing and disappearing in a dynamic environment. When the target medium is print, overflowing content may be printed; it is not defined where it may be printed.
auto: Like scroll when the box has scrollable overflow; like hidden otherwise. Thus, if the user agent uses a scrolling mechanism that is visible on the screen (such as a scroll bar or a panner), that mechanism will only be displayed if there is overflow.
In addition to what you've mentioned auto according to the standard is apparently better in this case because it hides the scrollbars when there is no overflow while scroll leaves them always present. In netsurf and presumably other browsers they seem to have the same effect because browsers aren't following the standard. Sorry about that, ```overflow: auto``` is a better choice.