I often see “needs to” where “must” is required.

Problem:
“Must” and “needs to” are not synonyms.

Explanation:
“Needs to” in a sentence implies that the subject of the sentence has needs.

I often see “needs to” in technical documents that talk about software applications “needing to” do this or that.

When it comes to “needs”, let’s compare people, non-human animals, and inanimate objects.

People have needs. American psychologist Abraham Maslow argued that people have a pyramidal hierarchy of needs. The base of the pyramid refers to “Biological and Physiological needs”, and the top of the pyramid refers to “Self-actualisation”.

Non-human animals have basic needs. All would agree that non-human animals have biological and physiological needs (such as air, food, drink, and shelter).

Inanimate objects do not have needs.

I believe that one place where humans often go wrong is to impose human characteristics on inanimate objects. For example, software applications do not “need to” do anything.

“Must” is the appropriate replacement for “needs to” in such a situation. For example, a word-processing application does not “need to” offer an undo feature, but one could say that a word-processing application “must” offer an undo feature (e.g., to satisfy a human requirement that mistakes in operation of the application can be corrected easily).

One more point: Imperative sentences are spoken or written when one human is imposing a requirement on someone or something else.

So the statement “You need to clean your room.” said by one person to another is inappropriate as an imperative sentence, although it certainly could be appropriate as a descriptive sentence.

The statement “You must clean your room.” would be appropriate as an imperative sentence, with one person imposing a requirement on another person.

In contrast, the statement “You need to clean your room.” indicates that the speaker or writer of the sentence believes that the listener or reader feels a necessity to clean his own room.

Solution:
Use “must” when imposing requirements. Reserve the use of “needs to” to refer to the basic necessities of humans and non-human animals and to refer from a psychological angle to the “higher” needs of humans in Maslow’s hierarchy of needs.