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In my view, this whole way of thinking is a bit problematic because it misses an important point: YaSM, ITIL and any other best-practice guidelines shouldn't be seen as something that we either "do" or "don't do". They are sources of advice, and we are free to decide which part of the advice works for us.
Nothing speaks against looking at various guidelines. Indeed, I suppose the best approach to finding good advice is to explore various sources. Then we can pick and choose what is applicable to our particular situation, and adapt the advice to our needs.
As for ITIL, I think there is nothing wrong with it in principle, because it contains lots of valuable and time-tested guidance. But ITIL can be a bit of a challenge, because it has grown immensely over the years as ever more content has been added. Making sense of this vast amount of information is not easy.
YaSM, in contrast, is less complex and easier to understand, especially for someone who is new to service management methods. But YaSM was not developed as an "alternative" to ITIL:
Everyone who knows ITIL will immediately realize that ITIL and YaSM have a lot in common. YaSM is thus ideal for getting started with service management best practice, while ITIL may be used as an additional source of specialist advice when needed.
Actually, I think it's fair to say that YaSM is very good at helping practitioners understand how service management works, which in turn enables them to appreciate and navigate the huge wealth of guidance offered in ITIL.
So it's not either YaSM or ITIL - both can happily coexist.
Ask questions and share your thoughts in the YaSM community.