Many years ago, I read a management article by some perky scholar who recommended saying "Yes!" whenever a supervisor or peer asks you to take on a new project. Think of the knowledge and the enhanced reputation you'll gain, the writer noted, when people regard you as the "Go To Person" on such matters.
That advice, of course, is idiotic. Always saying yes is as dumb as always saying no and there are plenty of people out there who will load you up with useless, career-killing projects. A few of them may even be your friends.
Some of the most pleasant memories that warm me on cold winter evenings are of the times when I fended off projects that were quagmires in the making. In many cases, people said I was crazy to reject the opportunity but it was usually not difficult to hear the slight tone indicating they didn't believe what they were saying. They were, as the expression goes, trying to sell me a bill of goods.
You have limited time and resources. Even if a project gives you more authority and staff, it may either distract your focus or walk you into troublesome territory. There is a reason why such properties are on the market and it helps to thump the walls and look for termites.
The "Go To Person?" I still smile at that one.