Is Sex really necessary?

[Njokime]

Sex is part of human nature, people are attracted to each other no matter the situation. People have sex even when there is a deadly pandemic. Personally I do not think the sex here was misplaced

[Bisqwik]

I think this issue is likely going to depend on your own stance for how sex is viewed. Aside from the cause and effect of the hormone producing plants, testosterone coming to mind, it could just be that dalliances aren't considered a big deal by Grant. Maybe its cultural to some degree. Now, necessary to plot in general I can't speak to. I think it entirely is a case by case basis. I've had books I loved have a sex scene forced in and it just jars me. Then again I have read books where sex was integral to the story, not in a pornagraphic way but in story and character development. Some of Piers Anthony's work comes to mind.
If sex to a person is meant to be hidden, is shameful in some way, or just looked askance at because of whatever societal influence, then sex scenes are going to be jarring and maybe out of place. Or won't be a disturbance to the story unless it's very out of place.

[zainherb]

It is human nature to have sexual urges and I think the author depicted the true human nature and I don't think it's for only readers who are fond of it.

I agree. It Is true human nature, and the author depicted it.
In many cases, in many books, sex scenes aren't necessary, but they're put in there anyway, for a variety of reasons.
And, sex sells, as they say.