In the third perek of Eruvin, the mishna and Talmud deal with which foods can be used to effect an eruv. The mishna states that Terumah (food only fit for a cohen) can be used for an eruv. The Talmud asks how can a regular person use Terumah, he cant use it. The answer is clear, a cohen can use it and therefore since it is useful to someone, it is fit.
The Shikkerdovid thinks there is a beautiful message here. The person of Eruv is to combine or blend homes or residences for purposes of carrying. What is more illustrative of blending than using a food that you personally cannot eat, but others in your community can use. In essence, it is not about you.