Could anyone tell me what the functionality of QwtPlotItem::setItemAttribute?

[picokuo]

Hi, Sir:
I studied the sample code of histogram, and change
setItemAttribute(QwtPlotItem::AutoScale, false);//true);
setItemAttribute(QwtPlotItem::Legend, false);//true);
, but I cannot see any difference.
Could anyone teach me what this API is used for?

Thanks a lot.

BR,
Pico