could someone please explain mame's [soft] reset?

[TheShanMan]

So in Donkey Kong a reset kills the high scores (I'm running with the hiscore patch and without save state) but in Joust 2 a reset leaves the credits alone.

Can someone explain what soft reset and normal reset do so that I can have at least a somewhat accurate idea of what will happen in any given game? Or at least the range of things a soft reset or a normal reset can do? And how the 2 resets are different from powering off a game (i.e. exiting the game and restarting without save state)?

I'm at a point where any time I want to try doing a reset I probably won't for fear that it may do more than I want (like wipe out high scores).

[SirPeale]

Depends on the game.  On a game like DK the scores reset if you power off.  Joust they're saved by the battery.

[TheShanMan]

But the highscore patch preserves high scores after a power off, and did Joust 2 really save the # of credits after power off (or reset)? Seems strange.

But that doesn't really answer the question. What is soft reset supposed to be? What is (normal) reset supposed to be? What is power off supposed to be (i.e. how is it different than the 2 resets)?

I understand power off - some games save high scores and possibly other stuff in NV ram (although it seems strange to save credits in NV ram). But when would someone soft reset a game rather than powering off? And when would someone (normal) reset a game rather than power off? That's what I'm trying to get at.

The kind of answer I'm looking for is something like "soft reset clears NV ram except for high scores, normal reset clears NV ram plus (in some games) high scores". It's obviously not that simple but there must be some logic to it, or at least there must be some intention that led to the creation of the soft reset and (normal) reset functions.