My conlang already has Benefactive and Lative cases, does it really need a Dative case? I'm racking my brain to find situations that couldn't be covered by those two and would require a separate Dative case.
Yours is a very interesting and legitimate question, but in the light of what we know from the languages of the world, what you ask might not be what you mean to ask. Let me expand a bit below.
To answer your question in brief: no, your language does not need a Dative, but yes, your language needs a device (or "construction" in Construction Grammar terms) to express the third argument (also called the "indirect object") of verbs that take on three arguments (subject, object, indirect object).
Now, whether you have separate devices (constructions, or in your case "cases", no pun intended) for semantically different indirect objects or not, that is up to you. Since you already have a Benefactive case that could express an indirect object (whether that is semantically a recipient or a beneficiary or else), then you can use that to express an indirect object that is a simple recipient. So, note that there can be a mismatch between syntactic arguments and semantic arguments (for example indirect object vs. recipient, benefactor, etc). Moreover, depending on what linguistic framework you assume, things can be slightly different. Here I am adhering to some form of (Radical) Construction Grammar.
For example, since you have a Benefactive case and a Lative case you could use the former in sentences like "I gave the book to the man" and "I opened the door for the woman" and the Lative case for "I went to the market" and "I am throwing a stone at you". But again, that is really up to you, as also hinted at in other answers/comments.
The drafts of the first two chapters of Croft's Morphosyntax: constructions of the world's languages expand on this. See https://www.unm.edu/~wcroft/WACpubs.html.
Your lang, your rules. But generally speaking, no, you don't need a dative case.
Funny thing is, you don't even need a dative case even if you were to wrack your brain and come up with handfuls of potential situations! Languages are funny that way. Those sneaky native speakers will just come up with some clever way of handling things!