Understanding coupling caps

Hi.
I have been designing opamp based, battery operated headphone amplifiers for a couple of years now.
Recently been delving in dual supply designs. I'm struggling getting to grips with coupling capacitors in this regard.
Where are they needed when working with dual supplies/split rails? Where are they not needed?
I will be connecting some opamp stages together. Buffers, going into gain stages, going into some more buffers.
There will also feature some volume pots between stages.
Do I need them right at the input of my amps too?? Can I leave them out all together (dc coupling)?
Any help will be appreciated...

An opamp has an input offset voltage. It might be plus or minus 6mV. If the DC gain of the opamp is 100 times then its output will have a DC offset voltage as high as 10mV x 100= plus or minus 1V which will mess up a volume control and/or mess up the next stage.
Show an example of your schematic and we will show you where coupling caps are needed.

Your coupling caps are basically required if the input offset voltage is significant or can't be nulled by another means.

In any event, an RF filter at the inputs may or may not be required. The output of a preamp may or may not be DC coupled. The LP filter of say 0.5 HZ should be built into the power amplifier. Depending on the OP amp, you may want to roll off the audio at 100 Khz maximum, so accidental RF (rectification at the OP amp inputs) doesn't overload anything. The above comments are for very high end stuff.

Remember the bypass caps.

Really high end stuff would use differential inputs that could be provided by XLR type connectors.

Coupling caps can be eliminated by the choice of OP amp.

Basically you need a coupling capacitor when you have AC signals that go from one DC level to another, such as the different bias voltages between the input and output of a transistor amp. For an op amp circuit you may need them if the gain is high causing the output offset voltage to be high as AG mentioned. Alternately you can use an op amp circuit that has low DC gain but high AC gain to minimize DC offset at the output.