When you are the XYZ guy this opens doors that are closed to others, if you are the specialist in selling high value real estate you are far more likely to get that high value real estate to sell than someone who is not.
If you are a specialist mechanic for European cars then you are far more likely to be chosen to repair someone’s pride and joy than joe mechanic down the road. The trick with specialisations is a lot like creating great products, it needs to be high value and unique. Choose something that matters, something that matters to your boss, your customers, whoever pays your cheques and let that specialisation open doors for you.
It’s important to find some aspect to be passionate about, passionate people are naturals at selling their specialisation. You could be a fantastic chef, but if you are not passionate about it, you will never make it because people can see you are not passionate about it.
Be the one who knows more about it than anyone else, research your specialisation, study it, take it home, read books about it, practice it and become more knowledgeable than anyone else. Be careful though, stay too long and you can become a one trick pony. Being just a one trick pony is dangerous because too many jobs become redundant as technology and demand shifts over time. You only have to look back in recent history to see the job of the “type writer” has completely disappeared.
Keep your parachute handy, sometimes you just need to make an exit. One way you can tell if it’s time to leap is if you can’t make your specialisation compelling to someone else it’s no good.