I personally do not see the harm in itemizing my bids. Some contractors think that by itemizing they are giving away too much info maybe.
Is good to itemize as i have found out that sometimes the job needs to be broken down into different phases. However i do draw the line if the customers ask for a super itemized quote i.e (labor,materials,profit,additional expenses how much if i help, how much if i dont, how bout if i feed you,cost of 5 different brand of windows etc, etc)......you get the point
...not because i mind letting my customer know how much i make as it usually turns out to be double the product cost. But because free estimating is very time consuming an like the word says is free so i find and usually my customers do too that a per window cost (including installation and materials) is sufficient.