When to use Map and when element-wise ops?

Question

I'm comparing XLA's xla::Map and element-wise ops, and I'd like to work out when to use each.

API

On a quick glance, it appears that all computations on scalars can also be defined for arbitrary shapes since all relevant ops have element-wise variants (Eq, Sin, Add etc.). I'm not clear what Map provides other than an alternative API. Or is it simply so that we can use a pre-built scalar computation, in which case how does it differ from Call?

Performance

Does xla::Map have the same performance characteristics as element-wise ops? That is, in pseudo-code, are

Map(x, Abs)
Map(x, compose(Neg, Abs))
Map({x, y}, Eq)

optimised at least approximately as efficiently as

Abs(x)
Neg(Abs(x))
Eq(x, y)