[MichaelGG]

Example:

  let x = let x = 1
          x + 1

If you use tabs the indentation is broken depending tab size. Some languages prefer needless symbols to do this; I prefer the cleanliness of just whitespace.

[rascul]

The indentation is fine, the alignment is broken. Tab to the indent level and align after that with spaces.

[MichaelGG]

The actual indent level is wherever the second let begins. It's equivalent to:

  let x = 
      let x = 1
      x + 1

Seems inconsistent to have to use a mix of tabs and spaces in different scenarios of visual preference.