it depends on how you listen to music. if you like to listen full blast all the time, then soft clipping is a good idea and will lessen the chances of frying your amp or blowing a speaker.
if you never push your amp hard, then defeat the soft clipping as it just adds another device in your signal chain that adds a slight amount of distortion.
with my older NAD, i defeated soft clipping when i used it as a stereo reciever but turned soft clip on when i used it to drive my subwoofer.
i also noticed that the "low level" button that increases the amount of volume knob turning needed to max volume also softened the treble slightly for the same audible volume level.
a good rule of thumb in hi-fi is "less is more". the more things you add to any system, the more complicated it becomes and the more things that can go wrong with it.
that's why some audiophiles are diehard "small two way speaker only" fans and why there was such a big buzz over "passive preamps" a while back. passive preamps remove EVERYTHING from the signal chain except for the volume knob. there are no amplifier stages in a passive preamp. the upside as they remove the least bit of information, but the downside is that they can't boost the volume for low level (line only) signals and have no phono capability. in general, tone controls are also looked down upon in hi-end preamps. if you can defeat them, you'll get purer sound there too.
the fewer things in your signal chain, the fewer things there are that can go wrong.
do an a/b test with soft clipping. if you hear no difference in sound, then leave it on. it protects your speakers, but it limits your dynamic range and makes your music etc. more compressed.
the sound without it will be truer to your source material.
Personally, I would rarely use it. If your amp is clipping you need to turn it down and if your speakers are distorting you need to turn the amp down or get new speakers that can handle the power. The soft clip feature will ultimately shut down the receiver if pushed too hard.
The only time I would use the feature would be during a party when others have access to the volume control and I am not there paying attention.
Correction Gregory, distortion is due to the amp not being able to provide more power. Changing speakers has got nothing to do with it.
Bottom line is, if one knows what the soft-clip feature is for, one would know when the amp is clipping and would reduce the volume, thereby should keep softclip off. If one dosen't know what the soft-clip feature is, one should keep it on and not worry about clipping.
Jaggu-- While an insufficient amp going into clipping is the more common reason for speaker distortion and eventually speaker damage, there are many instances of having a person with a far more powerful amp playing speakers too loud and frying them.
If a person with a powerful amp (relative to the speakers power handling capability) insists on playing speakers as loud as they'll go, you can manage to burn 'em out.
The only real defense against frying a loudspeaker is to listen closely to how it sounds. You'll hear clues -- maybe not the instant the speaker or amp starts to distort, but long before damage is done. Telltale sounds include the sound of a woofer rattling its basket or the hazy, whitish sound of a tweeter going hypersonic.
One doesn't need a soft-clip feature to know that either the amp is clipping or that the speakers are being played too loud (too many watts) for their voice coils (on midranges and woofers) and causing the tweeter to go hypersonic.
it's always better to have too much power than not enough. MOST speakers blow because their amp is driven too hard. once an amp runs out of steam, it starts to clip which is the main reason that speakers blow.
as stated, when music starts to sound distorted, turn the volume down. i've heard so many knuckleheads push their systems into unlistenable distortion just to hear it louder.
volume levels also fall under the "less is more" rule. less volume = less distotion AND hearing damage. audio knuckleheads are probably so deaf that they can't hear distortion anymore.
it cracks me up when i hear a car system played so loud that the speakers actually buzz with distortion or you can hear the car's bodywork slowly falling apart from vibration.