Based mainly on this post:
I came here looking for the same answer.
I think that Lookup() might be a bit dangerous since it may cause new users to satisfice with lookup rather than learning thisRow semantics which are really much simpler and more powerful.
Maybe in addition to the recommendation to use Filter the tooltip could say:
Categories.Lookup(Name, Sales)
is the same as
Categories.Filter(Name=Sales)
and the filter is easier to read
Or something like that.