This caught us out recently where code did a strict type check for `myVar === undefined`.
The var was defined as `let myVar;`, without a value - so the check returned false (it's `null`).
To avoid this situation, we've decided to enforce declarations with values.
Note that preference should be given to single, immutable assignments via const where possible.
See http://eslint.org/docs/rules/init-declarations
Ingo Schommer