The title of this poem gives us a hint about the main subject of this poem—the Lotos-eaters. But who exactly are those Lotos-eaters? Well, it could refer to the sailors, who arrive on the island and make the mistake of chomping on some Lotos. Or Tennyson might be talking about the people who the sailors meet, those mysterious "dark," "pale" natives who give them the Lotos in the first place. In a way, as the sailors transform in the poem after munching the Lotos, the title can be understood as describing both the natives and the sailors.
The title also tips us off to the poem's connection to an even more famous piece of literature—Homer's Odyssey. This whole poem was inspired by an episode in Book 9 of the Odyssey, when Odysseus and his crew, trying to get home to Ithaca, wind up in the land of the Lotos-eaters instead. Using a title to allude to another work is actually a pretty common literary trick. It's a pretty easy way to class things up a little, to latch onto the prestige of the famous literature that came before you.
So actually, this title does a lot. It tips us off about the plot of the poem, describes all the main characters, and lets us know something about where it's coming from. That's a lot of work for one title to take one. We wonder if it might want a nap…