Combining Prayers

When combining prayers like Dhur and Asr, is it more preferable to pray them both at the Dhur time, closer to the Asr time, or somewhere in between? Sayyed Mohammad Al-Musawi	How can I maintain the practice of praying each prayer separately at its designated time, even though the majority Shia mosques combine Zuhr-Asr and Maghrib-Isha prayers? Sayyed Mohammad Al-Musawi
Is there any evidence specifically from Shia sources that confirms that the Prophet (pbuh) used to combine his prayers even when not in a state of emergency? Sayyed Mohammad Al-Musawi	Why do the Shia insist and prefer combining prayers, which is a permissible method, over the regular method which is to offer each prayer on its time? Sayyed Mohammad Al-Musawi