Our Sunni fellows get surprise when shia pray Dhuar and Asar together and Maghrib and Esha’a together. But they dont know it is all proven the Sunnah of the holy Prophet (pbuh) which mentioned in Sahi al Muslim.
Please find the narrations.
These narrations are very well self explainatory, that holy Prophet comnined two prayers without any fear or any emmergecy.
The narrations says itself, it is to keep away people from unnecessary hardship. We can experince this in our daily busy life.