Tutorial - Modeling Turbine rotor in SolidWorks?

Here is the tutorial.
Step 1:
Right Plane>>Sketch.
Step 2:
Draw this sketch.
Step 3:
Revolve it about center line.
Step 4:
Front plane>>Sketch.
Step 5:
Draw this profile.
Step 6:
Extrude it mid-plane.
Step 7:
Select top plane & origin and then click reference geometry>>axis.
Step 8:
Circular pattern.
Step 9:
Select the boss-extrude as feature to pattern about axis1.
Step 10:
Insert>>Features>>Flex.
Step 11:
Flex input be the body. Twist type and then enter 60º. Click OK.
Step 12:
Front plane>>Sketch.
Step 13:
Draw a circle.
Step 14:
Revolved cut it about the axis. We have the part.
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Why are you cutting the blades at top? What's the purpose of that hole
Thank you bro