ag.algebraic geometry - Nature of Invertible Sheaves in which there are no global sections.

They can still give you (non-canonical) rational maps to $mathbb{P}^n$:

Even when an invertible sheaf $L$ on $X$ has no global sections, one can still find open subsets $U$ of $X$ such that $L|_U$ is globally generated, for example when $U$ is affine. This isn't so interesting, but if you can find such a $U$ that is not contained in an affine, then $L|_U$ might not be trivial, and then you might get morphisms from $U$ to $mathbb{P}^n$ (by choosing generators) not coming from $mathcal{O}_U$. If $X$ was integral, then $U$ will be automatically dense, so you get a rational map from $X$ to $mathbb{P}^n$.

One way you could look for such a $U$ is to pick $n$ elements of the stalk $L_x$ at a point $x$, then intersect $n$ neighborhoods on which these elements extend, remove their common zero locus, and let the result be
$U$. If $U$ isn't contained in an affine, maybe you've found something cool. If you really wanted you could try working out a nice description for the rational map you've defined (though I've never done this). Even if $U$ was affine, maybe you've found a more interesting description of a less interesting map.

From a very different perspective, since $mathcal{O}(-d)$ is the inverse of $mathcal{O}(d)$, in some sense any "information" it contains is obtainable from inverting the transition functions of $mathcal{O}(d)$... so with this restrictive view of "information", perhaps it would be interesting to study what sort of morphisms/maps to $mathbb{P}^n$ one can get from an invertible sheaf $L$ on $X$ when neither $L$ nor $L^vee$ is ample/very ample.

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