I have been teaching Plato on the three beds (his critique of the imitative arts in Book X of the Republic), and the question that comes to mind is "what role can Plato's theory of Forms play for us?" A reasonable first response is that Plato might well be right that there is an eternal unchanging Form for mathematical entities. The argument that the perfect circle is the only circle and this the things that represent the circle or are called "circle" in our world are not really circles...is plausible. Still, it is less convincing that there is such a thing as the perfect bed or even a correct and unchanging definition of "bed." Equally implausible is that there is a perfect State, although clearly Plato thought so, as in the perfect State would be one in which the three classes were in harmony, the philosopher-kings ruling. We can at the very least see talk of perfect Forms as simply talk of ideals (or perhaps as replaceable with more common-sense talk about ideals). So the craftsman who is interested in making good tables can reasonably be expected to have some ideal in his/her mind and be dissatisfied with his/her table to the extent that it does not meet the ideal. These ideals would not be eternal and unchanging or even universal. However the notion that one could always make something better or closer to the ideal might itself be universal.
At the same time, it is not clear that arguing over the nature of the perfect table or trying to come up with a definition of "table" would be of great use to a table designer. One possibility in all of this is that we can have a definition that has no real normative dimension. In discussion "table" my students suggested that a table must have a surface that can be used for writing or eating (the two main functions of tables) and must has some support to be sufficiently above the ground to serve this purpose. The definition I have found on "The Free Dictionary" online is "An article of furniture supported by one or more vertical legs and having a flat horizontal surface." This has the advantage of classifying it under a genus, i.e. furniture, but does not mention anything about its purpose. Moreover, some things can rightly be called tables that do not have any legs. Even the flat, horizontal surface is negotiable as long as the item serves the purpose of a table. But then "serving the purpose of a table" is not the same as being a table. A chair or a bed can be used for writing or eating on, but this does not make a chair or a bed a table (even when they have one or more vertical legs and have a flat horizontal surface!) Still, if you are a table designer and are trying to make the best possible table, as I have suggested above, none of these definitions are going to help that much. You are probably going to also be thinking of things like excellent craftsmanship, a perfect rendition of a certain design type, and quality of materials, as all going into the quality of your table - and these things just do not appear as features in any of the definitions on offer. So perhaps one could drive a wedge between the notion of the ideal table and the notion of the ideal definition of a table. In short, although I had thought that having a normative dimension to one's definition (for example, giving the function) would really help non-philosophers do their tasks, I now suspect that the ideal X incorporates a lot of other things than just the function (although functionality is still important.)