Slider anchors/nodes must not be used to manipulate slider speeds (whether they are normal nodes or red ones). Using extra nodes to make a slider "wiggle" is usually fine, but using so many that the slider gets scrunched up (which also makes the sliderball go crazy) or become a "hold slider" is abuse of the hitobject's intended use and is not allowed. AIMod (shortcut ctrl+shift+a) will also point out sliders that move in an "abnormal" way, so make sure to check that if you're unsure of a slider.This is the actual rule, and it's here to prevent people from making unreadable sliders like on this map http://osu.ppy.sh/s/79725 or sliders that make you 100% lose the combo like this one (Blue Dragon's Big Money's one, it holds for 1600ms).
I think that hold-sliders should be allowed if they cause no harm to the beatmap's playability - for example, they could be allowed if the hold time is less than 200ms or if they are performable by just holding the cursor on slider's head.
Some hold sliders fit in the song so perfectly and play so good that they are impossible to replace with something else without losing the fun and awesomeness they provide.
I would suggest a change like this in the rule:
Slider anchors/nodes must not be used to manipulate slider speeds (whether they are normal nodes or red ones). Using extra nodes to make a slider "wiggle" is usually fine, but using so many that the slider gets scrunched up (which also makes the sliderball go crazy) or become a "hold slider" is abuse of the hitobject's intended use and is not allowed, unless the hold time is less than 200ms or the slider can be performed by holding the cursor on slider's head. AIMod (shortcut ctrl+shift+a) will also point out sliders that move in an "abnormal" way, so make sure to check that if you're unsure of a slider.
Extra: regarding this
AIMod (shortcut ctrl+shift+a) will also point out sliders that move in an "abnormal" way, so make sure to check that if you're unsure of a slider.I've never seen AIMod pointing out any slider as abnormal, is this still implemented? Or according to this rule, any slider that does not trigger AIMod would be rankable