As someone who had been using PureData for quite a while the idea of having that kind of development environment integrated into the DAW was super exciting, unfortunately the actual implementation leaves a lot to be desired; personally the final straw was when I realized that the Max process space was global to Ableton so that global variables would leak between devices (no sandboxing)... This may have been addressed in further releases as I was a very early adopter, but all of the other issues pointed out by the other posters still stand.
If you're looking for a platform agnostic alternative to Max4Live there is PlugData[0] which is a VST implementation of PureData -- the open-source origin of Max and created by the same authors.
And there is the Grid for Bitwig[1] which offers a modular graph based MIDI/DSP programming environment that runs at audio rate and is fully integrated into the DAW as a native solution! The Grid is somewhat limited as it isn't extensible, but it supports >95% of common use cases and is used internally to build Bitwig's native devices. Hopefully in the future Bitwig will extend it's open API surface to include building custom Grid modules -- in the meantime PlugData is perfectly acceptable patch for doing unusual logic calculations and doing left-field things like interfacing with robotics :)
[0] https://plugdata.org/ [1] https://www.bitwig.com/the-grid/
(I wrote Scheme for Pd, which puts a scheme interpreter in Pd)
It's fantastic for controlling the Live API because the way the Live API works is you identify things you want to control with lists of symbols. This is far more pleasant in Scheme than either in Max, JS, or Python (your other options in Live, though Python is not officially supported for non-device vendors).
While Live has many warts, and I wouldn't want it to be my only DAW (I also use Reaper), the Live API lets you do things you can't come close to any other pro audio software (yes, including bitwig and reaper). Being able to have my sequencers interface with the entire app is incredibly powerful.
Here's the project page and youtube page if you want to check it out:
YouTube: Hacking Live with Lisp https://www.youtube.com/watch?v=j0sKBA-Pv2c
Scheme for Max on Github: https://github.com/iainctduncan/scheme-for-max
I also ported csound~ for Pd to Max so one can mix csound in with Scheme and Max seamlessly. https://github.com/iainctduncan/csound_max
I don't really use Max that much anymore, since ultimately the benefit is that it's supposed to be easier to use than C++, but I find that really hard to believe in my experience. Another supposed benefit was supposed to be that Max came with a bunch of UI and DSP stuff built in, but they seem to have now neglected that aspect of the software and instead creating new projects like gen~ and RNBO (I'm not sure what the point of RNBO is). The thing is, JUCE gives us all the stuff that it was cool that Max came with 2 decades ago, plus more, while being less buggy and able to create production quality plugins.
I think the ultimate staying power of Max is simply due to it having aesthetic weight in the artistic community. It's still the "cool option" for the interactive art exhibition crowd. Other than that, the only thing really keeping it alive is Ableton...
Max is still a great piece of software, but these days, just learn to code.
In the long history of Max, I can only think of a couple of things I've liked that were made with it, and they were both for Max for Live. I think the fact that they were made with Max was just incidental — it's the easiest way to add MIDI effects to Live.
(For anyone who answers with "but you can just write JavaScript now to do everything in it" — running MIDI events through its JS nodes defers the events to the non-timing-critical thread, ruining the timing of the MIDI events.)
BTW, my Scheme for Max extension does run in the timing thread, if you want to write sequencing code in Max. I basically did the same thing they did with JS (lock it to one thread) but let the user choose the thread and let the user control when the GC runs. It works suprisingly well for sequencing - locks in with Live completely if you trigger things with plugsync~
As someone who works in all spots on the spectrum, I would personally never say "just learn to code". My music rig includes Live, Max, C code, Scheme, and eurorack. There are parts in each layer that are vastly more efficient to do in that layer. (Many years ago I did do it all in code, and wouldn't go back)
In the end I shifted to doing as much as possible in Eurorack which feels a much more creatively enabling and stable platform, relegating Ableton/Max to covering what's left.
Yes you could quite easily write plugins nowadays but you can't really embed them into the DAW itself, using floating windows instead. And you can't really make them look native easily.
OTOH you can create Grid devices but they're not as sophisticated as Max. And you can't explicitly code them.
