Yes, I think it is an idiom. It means that it was wonderful. It is usually used to refer to something that energises you, or makes you better, or very happy. It might refer to a holiday, or even something as simple as a well-needed drink.

Nerea: Yes this is idiomatic. It is a measurement of how much good something will do for you. One might understand it as part of a scale in which there are 2 EXTREMES at opposite ends of a spectrum and there is a MEAN or MIDDLING VALUE. The World of Good is one exteme and at the opposite end of the spectrum of value would be No Good At All. . It is commonly used in scenarios like this. You have been working too hard without much rest. I think you should take a few days vacation and visit the beach and enjoy the sunshine, fresh air and water. It would do you a world of good. .

"It helped us very very much" " It helped us a whole lot" "We really needed that" That time off did us a world of good! We really needed to have that holiday!

thanks. Really learning the idioms are very complicated for me. Moreover, when I have to do a writing in the exams, It is very important putting some of them. This one I have to learn now and I try to put it in my exam. For example If i am speaking about my last holiday I can put the sentence, can´t I?