How to cut holes throughout the curved surface of a cylinder?

You can try this without add more planes

  1. Step 1:

    Draw cylinder in symmetric plane

  2. Step 2:

    Draw hole to cut on Front Plane

  3. Step 3:

    Select Extruded Cut features, then activate both direction, Direction 1 & 2, from drop down box, select features 'Through All' for both direction, then click ok

  4. Step 4:

    Select circular pattern, and follow instruction in pictures. :)