Why DataEngine::containerForSource use is discouraged?

[Yuri Baranov]

Hi, everybody!
The documentation
http://api.kde.org/4.x-api/kdelibs-apidocs/plasma/html/classPlasma_1_1DataEngine.html#a623f9becf3d4a464a64ce0ee2f8fa70d

says:

> This method should not be used if possible.

I've browsed source code of some dataengines (e.g. microblog, rtm) -
they do use the method.

I wonder, what is the reason behind the recommendation?

Yuri