Correct. You would use it with no lacing.
That goes back to my first statement of lacing and list levels doing different things. List levels is kind of like list comprehension. It tells the node to treat a specific list level (sublist structure) like it’s the input being passed to the node and to iterate each list or item at that level individually.
In your example, the + node is already going to iterate over each item in the inputs. By default (auto) it’s going to match lengths, same as shortest lacing. Longest lacing is going to continue iterating with the last value in the shortest list (to match the longest). Using @L1 with longest (or shortest) lacing won’t change anything since the node is already iterating through each item (@L1). Using auto (no) lacing with @L1 allows the node to treat x as a list and y as a single input, iterated for each value, with its natural comprehension.