Skills are a tricky thing to really know. On the one hand, you have obviously got a pretty solid idea what you are capable of doing (since you have most likely been on the job for awhile at least. But on the other hand, you have also got a lot of different possibilities as far as what your skills might translate into. For instance, a good tile setter could potentially also do especially good trim work, and even skilled finishing work (such as finishing the trim of a high end custom doorway). Until you have tried a particular area, you can never be entirely certain that the skills which you already have would not be easily transferrable into another discipline, possibly in an entirely different section of a home or a business. This is why it can sometimes be beneficial to you to try helping out a lot of different skilled trades people, if you are thinking about changing trades or adding a trade into your tool box.
For one thing, there are going to be some occasions in which, no matter what your skills might be, there will be a lessening of demand for them. While some skills (such as being able to fix heating systems) will always be somewhat in demand, sometimes even they go through a bit of a slump (such as when there is a glut on the market for their services). In the building and service trades, it very often pays to have a few extra sets of skills that you might not use every day, but which you can whip out if ever the need should arise.
Consider the possibilities, if you happen to find a great client whom you can easily read. If you have ever had the kind of client relationship in which you can finish their sentences, and suggest things to them that they never even thought of (but end up absolutely loving), you know how great it is to be able to find more things that they need which you can do. The more skills you have here, the better.