Hollow Blue Squares complete rules?

[steven777]

I understand you subtract them from the yellow tetris block shapes.

But do the hollow blue squares need to be attached to / included in the final tetris shape you make?

And do you have to use all the hollow blue squares in a puzzle or can you ignore some if you don't include it in the final tetris solution shape?

Hope that makes sense. Thanks

[MASTAN]

All hollow squares must be used.

[Pesky]

Hollow blue squares must subtract from one of the shapes shown elsewhere on the puzzle board. And as MASTAN wrote, you cannot ignore any of them.