“X will do Y” vs. “X does Y”

Question

I have already asked the question “X won't Y” (able/willing) vs. “X doesn't Y”, and now I want to extend the question to further meanings/usages of will (according to the Cambridge Advanced Learner's Dictionary).

So, the question is if the following example sentences can be rephrased by plain verb forms instead of will. And if yes, is there any meaning difference between the original and rephrased version of the sentence?

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Meaning: ALWAYS

Accidents will happen.

Fruit will keep longer in the fridge.

vs.

Accidents happen.

Fruit keeps longer in the fridge.

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Meaning: ORDER

Will you stop being such a pain?

You'll go upstairs and you'll go straight to bed like your father told you!

vs.

Stop being such a pain!

Go upstairs and go straight to bed like your father told you!

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Meaning: ABLE

This quantity of lasagne will feed six people.

vs.

This quantity of lasagne feeds six people.

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Answer 1

Depending on context, "will" is generally a qualifier, meaning that it adds some ambiguity to a statement. For example, suppose someone asks, "What time will the sun rise tomorrow morning?" I can answer either:

The sun rises at 6 am tomorrow morning.

The sun will rise at 6 am tomorrow morning.

If the focus is on the sun rising, then there is no ambiguity because it is a natural event that will inevitably happen. However if we are focused on the exact time of the event, then "rises" sounds more certain. As an alternate example:

The Patriots lose the Super Bowl this year, as they did last year.

is completely unambiguous, so much so that it sounds as if I'm able to see the future.

In a similar way, as an order/request, "Will you stop being such a pain?" is a kinder than "Stop being such a pain!" although more that it's phrased as a question rather than as a statement. Another example:

Will you get me some milk from the kitchen?

Get me some milk from the kitchen.

Again, tone and context are important. Even if I don't add "will you", if I pitch a request as a question, then it's as if I did add "will" or "would" or "could", especially with someone familiar.

Statements of ability or capacity are the same as the others. "Will feed" is slightly less certain than "feeds", but in many contexts the difference is too subtle to matter.