It's not a "must", you can score well without it, but it is technically a structural requirement, so it's better to get it out of the way just in case your assessor is fussy about that sort of thing. It'll also be the last thing your assessor reads, and if they're on the fence about whether your essay is a 7 or an 8, for example, the conclusion will be what pushes it over to one side.
Try not to just redundantly restate contentions, never summarise the article or list all the techniques, and don't rank them by their persuasiveness. What you can do is comment on why a particular technique might be effective given a certain audience or context (eg. if one author makes repeated appeals to our sense of responsibility, we are more likely to share in his view that children need to be protected...)
Or just comment on how language is used generally; this can be a good place to sum up tone too.
Juxtaposition is as above (eg. when the herald sun put a picture of tony abbott's creepy winky face next to a group of students protesting about how ruthless and sinister he is)
A dichotomy is when the author attempts to split the audience in two. But rather than have it be an even split, they're usually trying to make one side look as bad as possible while making the other (their side) look as good as possible. It can be seen pretty much any time the author uses inclusive or exclusive language. So basically, at least once in most articles, but like any other technique, you have to do more than just point it out.