This is the 15111th most frequent Russian word.
полезны
Useful.
The word 'полезны' is used to indicate the health benefits or positive attributes of vegetables in terms of their impact on health.
Овощи очень полезны для здоровья.
Vegetables are very good for health.
Here, 'полезны' expresses the usefulness or practical benefit of advice given by older individuals.
Советы старших всегда полезны.
Advice from elders is always useful.
In this sentence, 'полезны' conveys the positive effects or advantages of swimming lessons for children's development.