There is absolutely a benefit to lazy if you're doing more than one combinator even if you ultimately need to iterate over the whole list such as the join case.

The lazy version basically turns into

   a = ""
   (1..1000).each { |i|
       next if i.odd?
       i *= 2
       i += 1
       a << i.to_s.reverse + ", " # ya ya, trailing comma
   }

Where as the non lazy version turns into:

    odds = []
    (1..1000).each { |i| odds << i if i.even? }
    doubled = []
    odds.each { |o| doubled << o * 2 }
    incremented = []
    doubled.each { |d| incremented << d + 1 }
    strs = []
    incremented.each { |i| i.to_s }
    a = ""
    strs.each{ |s| a << s.reversed + ", " }

Which means that you have you went from N iterations to 5*N iterations, with 5 intermediate arrays in this case.