This subject comes up a lot here. " Don’t need no stinking ___________" . Making a decision about what is needed or not needed at sea is not just a matter of coming up with some scenario where it might be needed, finding a substitute for that tool or whatever.
It’s all about trade off. Evey tool, instrument, procedure or resource added to a vessel carries a cost. The question is does the benefits outweigh the costs?
An example is voyage planning. The trade off there is that the time and effort spent planning, at some point, is better used doing something else. However the principles apply to just about every decision regarding time or money.
Not really just about hatch tents, I tried to make this point on another thread but made the mistake of putting “bow thruster” in the title.
This has come up many times. For example a person navigating needs a method to determine direction but it can be done visually. Better question is does a vessel need an additional tool (a compass for example) or method? Answer is it depends.
Other examples, additional sextant training for the crew, addition of an anemometer, adding a bow thruster, another crew member etc.
In each case the cost / benefit has to be thought of “at the margin”.
This thread is about when an equipment upgrade is justified, didn’t recognize at the time it’s about being 'at the margin"
Another is the “swing meter”
Nobody told this guy he didn’t need a swing meter because he could just eyeball it. Evidently when pushing barges up the river it good to be able to see subtle changes in rate of turn. Who am I to say that’s not the case?
Here’s a post using the same concept but in a different context.
"But in a sense it doesn’t even matter what the reason is; the high prices are telling you that California is perceived as a very desirable place to live, at the margin."