When I had GCS, I was told to remain off hormones a month before surgery stay off until a month after surgery by my endo. The surgeon wasn't as strict with the restart time and would have let me resume hormones sooner. I figured it was better to be safe than sorry so I remained off hormones for the full month after surgery.
The primary problems is clots can form in your body if you are inactive. The have occurred in people during long flights and that's why they recommend if you are on a long flight, you get up and move around during the flight. Now they have compression leggings that help but it's desirable to reduce the risk as much as possible. There is also another possible problem and that is some surgeons may not use compression leggings raising the risk.
Do clots happened all the time - no. It was normal for us to remain in bed 6 days after surgery and clots were not very common but they did happen occasionally. If you are likely to form clots, I would recommend that you follow the doctors recommendations.