Some artifacts are "useful," and some are mere art. Being "useful" means the building of such things allows you to build more of them, whereas an art piece doesn't let you afford any art you couldn't already afford.
If you obsess about making all your artifacts useful, you become useless. Extrinsic value and intrinsic value diverge. You make things that are valuable because they make more of themselves, but 0 * ∞ is zero. You have an endless supply of something that serves no purpose. Rather than accruing profits, you have wasted your labour.
When spending time on a "useful" device or technique, it must always be subordinated to "useless" ends. The point of money isn't actually to be accumulated. The point, ultimately, is to spend it. Once creating the "useful" artifact conflicts with spending the money, it is costing more than you're gaining.
Work to buy leisure. The more leisure the work can purchase, the more profitable the work is. Keep in mind that youthful years tend to be worth more than elder years. Discount future profits to taste.
Leisure doesn't have to be so-called unproductive, but it does have to be something you would do without being paid for, whether you can get paid for it or not. Indeed the work-leisure dichotomy seems like yet another trap.