Insane = maximum power available for acceleration.
Insane+ = maximum power available for acceleration plus battery conditioning (heats the battery to between 113F/45C and 122F/50C for optimum power delivery, mainly intended for drag usage.)
Ludicrous and Ludicrous+ follow the same pattern. Ludicrous mode was either a paid upgrade or an extra-cost option when new, depending on when your P85D was built.
Warning: the power is like a drug.