In this particular use case, yes, we don't need that, and that's exactly why the first version of the code that I wrote yesterdays didn't have liftables for values. 

However there's a multitude of other uses for tree <-> value conversions, e.g. https://github.com/scalareflect/interpreter/pull/8/files#diff-3fb462887cf14bd0ff5df477a1c37f65R236 or https://github.com/scalareflect/interpreter/pull/8/files#diff-3fb462887cf14bd0ff5df477a1c37f65R232. Doing that kind of stuff manually is much worse than smuggling values in tree attachments.