Context: I'm a consultant, in that I work for a company that does product and technology development for others (Cambridge Consultants, in the UK). I'm a generalist embedded software engineer by background, although I studied electronics. These days I mostly lead technical teams that include SW, FPGA, Electronics and Mechanics.
Not having a specialism is occasionally annoying. It makes my 'career path' less clear, I don't have anything particular to write down as my USP to clients.
In practice though these have been minor. My value has usually been that I understood all aspects of the system including cross domain. This meant that there were bugs that I could diagnose and fix easily that other people had no idea about (using an oscilloscope to diagnose software bugs is a useful skill).
As I became more senior and started running teams it became even more valuable because I understood what all the different disciplines were talking about and dealing with. It's a great advantage to architecting, planning and prioritising (some of this has been learning as we go along - I now know a fair amount about injection moulding despite being a SW engineer because I keep asking the mechies questions).
As other people have said, often it's about framing your skillset. Previously I have highlighted a relevant aspect of my experience as a specialism when talking to clients. These days I say "I am an expert in leading multi-disciplinary teams for product development".