thisArg in merge - really necessary?

[bergus]

The merge callback f is called with the this of the merge(…) call as the receiver. This doesn't seem exactly useful to me.
Are there any use cases? Does any code use merge.call(o, f, …) instead of merge(f.bind(o), …)?
Could we just drop this "feature"?

[briancavalier]

Not sure what I was thinking there :) Totally agree that f.bind(o) makes much more sense, and seems much more obvious. Let's drop it.