In considering semiotics and content analysis, content analysis only gives you the quantitative basis for the representations of things while semiotics show how meaning is created rather than what the meaning is. The structure of the meaning is deciphered by breaking down an advertisement, considering how objects and things work together to elicit a certain understanding. The audience, the combination of particular objects, and the absence of particular things work together in constructing a reality. In addition, culture and tradition are important to the context of an advertisement and breaking down meaning.
In my opinion semiotics are much more useful than content analysis in understanding how advertisements work. For instance taking into consideration an object in relation to the context of the setting. Perhaps content analysis looks at the number of revealing body images of women in advertisements. If the ad is for a swimsuit it is likely that a women is shown in minimal clothing, which could render it revealing. The quantitative aspect of content analysis doesn’t consider why the woman is wearing the bathing suit; maybe she is in a warm place, on the beach advertising a vacation spot, or, maybe she is in a car advertisement appealing to a male crowd. From content analysis we may never know. But these two different situations show how a woman in a bathing suit could elicit different ideals and without considering the semiotics, the content analysis becomes unrealistic. The combination of what is used in the ad to render a certain affect is essential to meaning; it’s silly to consider an advertisement without breaking it down and looking at how the parts sum up the whole.