Negative bpm was more like a glitch than a feature in Stepmania. That's why they removed it in Stepmania 4.
The implication is that an unintended feature is never useful to have, though, which is incorrect (negative bpm was an interesting gimmick - it could be abused, yes, but so can any feature about stepcharting, as NVLM et all show)
A good argument for its inclusion is that negative bpm is not a showstopping bug; it does not occur without going well out of your way to trigger it and will never interfere with normal usage of stepmania. About the only problem is that it will crash Stepmania if you play a chart that ends on a negative bpm, but this is trivially fixed (when loading a .sm file, check the last bpm change; if it's negative, treat it as positive). Another stepchart feature that can crash stepmania is the 'ghost hold end' which is a freeze end symbol without a matching freeze start.
i made a sim called "Sakura suck-u-all" - i think i made the BPM 99*10x9 : something massive - and when trying to start it - crashed SM everytime lol - so maybe it dont count cuz i cant even load it to play, but its what i got
The implication is that an unintended feature is never useful to have, though, which is incorrect (negative bpm was an interesting gimmick - it could be abused, yes, but so can any feature about stepcharting, as NVLM et all show)
A good argument for its inclusion is that negative bpm is not a showstopping bug; it does not occur without going well out of your way to trigger it and will never interfere with normal usage of stepmania. About the only problem is that it will crash Stepmania if you play a chart that ends on a negative bpm, but this is trivially fixed (when loading a .sm file, check the last bpm change; if it's negative, treat it as positive). Another stepchart feature that can crash stepmania is the 'ghost hold end' which is a freeze end symbol without a matching freeze start.
Negative BPM screwed up scoring. Any song that has steps that disappear will be impossible to 100%.
That's getting too far into accomodating a glitch rather than fixing it, though. To determine how many notes are actually possible to hit (AND where they are, for the purposes of the machine score) requires lots of extra processing and storage and someone would have to program it.
Myself I don't mind because it's not that big of a deal to me.