I need is what is needed and what is exact.
When used as an inflection of the verb need, it means what is indispensable. When someone says "I need", whether from someone or something, it means they can't do without to follow. "This must be done" represents that the situation is necessary and urgent, that it is important to stop and do what was asked.
"I need you" or "I need love" are both expressions of feeling and a request, an emotional need of the person.
"I need to say that I love you" is the title and an excerpt of a song by Cazuza, from the band Barão Vermelho. The lyrics speak of the love that one party feels for the other, but which the latter is unaware of. Therefore, it is necessary to reveal this feeling.
In a more practical way, it is also said necessary for everyday things, such as "I need these papers for tomorrow", within the work routine.
As an adjective, precise is the quality of what is perfectly accomplished. Something that is necessary means that it was done with rigor, in the exact measurements, in the way necessary to meet the need presented.
The expression "surgical precision" gives this idea of accuracy linked to the adjective precise. Doing it with surgical precision means doing it in detail and meticulously, without making mistakes or slipping anywhere.
Precise is also used as a synonym for categorical. It represents someone who is able to express themselves clearly and precisely: "she was categorical when she said no", that is, there is no doubt that the speech was negative.