Many couples, especially around the age of 50, choose to sleep separately for several reasons:

1. Improved Sleep Quality: As people age, sleep quality often declines. Factors such as a partner's snoring, teeth grinding, or movements can disrupt sleep. Sleeping separately allows each person to rest without disturbances, leading to deeper and more restorative sleep.

2. Reduced Risk of Infectious Diseases: In middle age, the immune system weakens, increasing susceptibility to infectious diseases like tuberculosis or skin infections. Sleeping separately can help minimize the risk of transmitting illnesses between partners, safeguarding both individuals' health. 

3. Maintaining Relationship Harmony: Sleeping separately can reduce minor conflicts arising from differing sleep habits, thereby preserving marital harmony. Additionally, having personal space allows each individual to feel more comfortable in their daily routines. 

4. Changing Personal Needs: At this stage, the need for physical intimacy may decrease, while the importance of quality sleep and health increases. Sleeping separately can better accommodate these changes, ensuring each person has rest that aligns with their individual needs. 

However, the decision to sleep together or separately depends on the relationship and habits of each couple. It's essential for both partners to discuss and agree on what ensures comfort and happiness in their relationship.