Do you mean the double-indent for the continuation line? That's actually in our style guide too: https://github.com/UWFlow/rmc/wiki/Flow-Style-Guide

The rationale is to delimit a continuation line from the block within it. For example:

```js
if (some really really really really really really really long condition &&
    some other condition) {
  launchMissiles();
}
```

You can clearly see that `some other condition` is not part of the true branch body.