By Widget I mean any object which is a QWidget and is bound by some other widget (so I do not count plain QObjects) that you need for your UI.<p>ListViews are optimized for display of lists, obviously, so they generally instantiate only visible elements in the view, and delegates do not even undergo geometry negotiation so they&#x27;re a bit lighter than a regular widget.<p>Still, if you do visualization or animation, the UI must respond within 1ms in order not to be noticeable, and that&#x27;s very hard to attain with Qt5.<p>I doubt people using QML on mobile devices really understand the issue either, since when mobile developers speak of &quot;animations&quot; they generally mean some random transition of the UI itself. Often, the operation is not even performed in the background, but rather simply sequenced (so that the animation appears to be smooth, but the actual delay is completely absorbed by the user). In these scenarios, times up to 250ms&#x2F;300ms might still be felt &quot;instantaneous&quot; as they&#x27;re shorter than the transition. For me, it&#x27;s outrageous.