It’s important to be multi-disciplinary. Not just as a diverse artist, but skilled in business, branding, sociable skills etc.
Is being a collaborative practitioner vital in today’s creative industries?
Not vital.
Collaboration can be an important tool in producing a successful piece of work in all senses as you have the combined assets of many people with different skill sets. This can make complex tasks much simpler, as everyone is pulling their weight, doing jobs that you in yourself would find difficult.
However, a collaborative effort can be a hindrance if you have a very set, single minded or specific goal. Everyone else’s interference could dilute the initial plan/idea. In addition, this could damage your own personal brand/uniqueness.
Being part of a collaborative effort could be an important step to becoming a horizontal artist as you would constantly be learning off of other people who are experts in their own right. For example, a photographer could learn a great deal from a graphic designer, who might teach the more about branding themselves as an artist. If not they have gained important contacts during the collaboration.