discerning between "all that" and "what"

Question

Although I have just googled, actually, I failed to get my specific answer, yet. I am wondering what is the difference between "all that" and "what".

For instance:

"All that I need is x."

Or:

"What I need is x."

Answer 1

"All I need" is used when you want to express the fact that what you need isn't much. You might say:

• "All I need is one more minute!"
• "All you need is love!"

"What I need", on the other hand, is used when you're simply trying to explain what you need, not how important the thing(s) are. You could have a list, or be in a position where what you need is irrelevant, all that matters is that you get something done, for example.

• "What I need is some more time."
• "I need his prosthetic leg."
• "I'll need several million pounds."

So, in summary, use "all" when you want to emphasize that you don't need much, and "what" when you just want to tell someone what you want.

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As @WhatRoughBeast said, beware of this being said ironically, or sarcastically. I'm not sure if this is difficult to hear in someone's voice when coming from a different language, though!

Answer 2

"All that I need" emphasizes that there is nothing you need besides the items you proceed to list.

"What I need" makes it clear that you need a particular list of Inge, but here might be other things you also need but didn't list.

"What I need is more time" means that you definitely need more time to complete something. You might need some tools or some money also, but you are stressing that time is the critical thing you need.

"All that I need is more time" is explicit that you don't need anything else, just time.