Being Useful at Work: Getting Used or Leveling Up?

I look at my employment as a pretty simple business deal. I get paid to perform a certain amount of time and effort on the job. I am being paid to be useful.

It's not "getting used", it's a voluntary value exchange. The moment that value exchange is no longer to my benefit, I'll move on. Equally, I expect that the moment that value exchange is no longer to my employer's benefit, I'll be let go.