Some folks who dive in very tight, confined areas (usually cave or wreck divers) consider the extra pull-tab on the spring strap to be a hazard. It can get caught on something and cause the fin to come off or get the diver stuck. Also, using the sleeve instead of nothing is safer for divers in these types of situation because it prevents any line the diver may be using from getting snagged in the spring.
Most divers will never dive in an area where this will be an issue, which is why we ship them with the pull-tab on, but leave the option to switch to the sleeve. Beyond this, it's merely a personal choice.