The center hole suspends the weight of the motor and yoke from the carriage on the saw arm. The four smaller holes you see in the photo receive the indexing pin to lock the yoke in the crosscut, inrip, outrip and accessories positions.
After years of use the indexing holes become a little oblong or egg-shaped. Some of the holes wear more than others because they get more use. You can align the saw to make an accurate crosscut, but the blade will heel in the ripping positions. I thought for a long time about how I could restore the accuracy of all of the holes. The key was to make each of the three holes used for precision settings (crosscut, inrip, outrip) capable of independent alignment. That can be accomplished with two pieces of strap iron, four 10-32 screws, and four nuts.
For further explanation, imagine you are looking at a clockface in the photo. 12 o'clock is at the top of the photo. The accessory indexing hole is at 1 o'clock. The inrip indexing hole is at the 4 o'clock position. The crosscut indexing hole is at the 7 o'clock position. The outrip indexing hole is at the 10 o'clock position. When you are ready to do the alignment, you will begin with the outrip hole, no matter how much wear it may have endured and how egg-shaped it may be.
Then you will align the strap iron plate you will make that lays above the crosscut indexing hole. Finally, you will align the strap iron plate for the inrip hole.