1. If there is no major difference

...but is there no major difference? Many musicians, and guitarists in particular, still have a general stigma against anything digital. Much of that is just superstition – by now, basically any analogue circuit can be emulated digitally so well that it's impossible to tell the difference. But that doesn't mean all digital effects, and particularly all presets, actually do the advertised job of getting you the sound you want. Or maybe they do get the sound you want, but only when playing a particular guitar and using a particular amp and can't really be adapted if that situation is different from what the manufacturer assumed.

2. a person who wants "Led Zeppelin sound"

but not everybody wants just something like that. Musician is a creative job, it's not about just copying something exactly as it has been done before (like, “it's not a creative artist you want, you want a bloody photographer”). With individual effects, it's very easy and literally hands-on to tweak the knobs, experiment with different orders of effects, etc.. And because you do that already whilst first setting up everything, and indeed also often later (because you played another set requiring different parameters, or merely because after transport the pots aren't in position anymore), you also readily get practise and a feeling for what the knobs are actually doing, so you know exactly which one to turn if you want to change the sound yourself in some way.
This is very different with digital multi-FX, especially with the smaller ones that have just a tiny display and one “data” knob. Then, particularly if the presets are actually good, most guitarist will just stick to those, maybe tweak one or two parameters, but never really develop an own sound.

Again, this doesn't mean it's not possible to create own sounds digitally – on the contrary, in principle DSP is highly customisable and with the right skill you could program it do produce completely novel sounds that really nobody has ever done before. Just, this requires a very different skill set from just changing pedal order and tweaking knobs, and almost no musician would actually do it.

1. If there is no major difference

   ...but is there no major difference? Many musicians, and guitarists in particular, still have a general stigma against anything digital. Much of that is just superstition – by now, basically any analogue circuit can be emulated digitally so well that it's impossible to tell the difference. But that doesn't mean all digital effects, and particularly all presets, actually do the advertised job of getting you the sound you want. Or maybe they do get the sound you want, but only when playing a particular guitar and using a particular amp and can't really be adapted if that situation is different from what the manufacturer assumed.

2. a person who wants "Led Zeppelin sound"

   but not everybody wants just something like that. Musician is a creative job, it's not about just copying something exactly as it has been done before (like, “it's not a creative artist you want, you want a bloody photographer”). With individual effects, it's very easy and literally hands-on to tweak the knobs, experiment with different orders of effects, etc.. And because you do that already whilst first setting up everything, and indeed also often later (because you played another set requiring different parameters, or merely because after transport the pots aren't in position anymore), you also readily get practise and a feeling for what the knobs are actually doing, so you know exactly which one to turn if you want to change the sound yourself in some way.
   This is very different with digital multi-FX, especially with the smaller ones that have just a tiny display and one “data” knob. Then, particularly if the presets are actually good, most guitarist will just stick to those, maybe tweak one or two parameters, but never really develop an own sound.
   
   Again, this doesn't mean it's not possible to create own sounds digitally – on the contrary, in principle DSP is highly customisable and with the right skill you could program it do produce completely novel sounds that really nobody has ever done before. Just, this requires a very different skill set from just changing pedal order and tweaking knobs, and almost no musician would actually do it.