Make Control Visible when Page Load

hi ,
i want to know some thing,
when i make control (visible=false) onpage load event, this mean this control is created and Make Load on Server? becasuse i have ajax html editor when i make it hidden onpageload event, all My Controls  rendered fast, but when i make it visible its slow down page , althouh ajax html editor is not in any updatepanel.
last question :
 
when any DataControl ( for example DataList)Contain Datasource (assume ArrayList) and This ArrayList is null , this datalist created ? and Make Load on Sever? and the speed of page is the same as there is no datalist?
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