How much warming up do you really need before lifting?

I sometimes wonder whether people spend too little time warming up or turn the warm-up into half a workout before the important sets begin.

Some lifters do a few minutes of light cardio, mobility work and several increasingly heavy practice sets. Others simply perform a couple of lighter sets of their first exercise and get started.

How much do you normally warm up?

Does your approach depend on the exercise? A heavy squat or bench press probably needs more preparation than curls or lateral raises, but it is easy to keep adding warm-up sets until they begin using energy that could have gone into the working sets.

I would be interested to know whether anyone has improved performance or reduced aches by spending more time warming up. Equally, has cutting back on stretching and general mobility work made your sessions quicker without causing any problems?

Do you follow the same routine every time, or base it on how stiff, tired or cold you feel that day? At what point does a useful warm-up become unnecessary extra volume?