I dont know what species you are talking about,but with Phelsuma they are located on the necks.It is usually the females but males can get them too.
I have a male thast has large sacs and I fear that they will never go as he has had them since I bought him about eighteen months ago.In my opinion he was given too much calcium(in liquid form?),but this seems to have decreased the calcium in his other bones.So all in all I dont believe that its good in males.