After the reception of the Sacraments, when we feel the love of God growing cold, let us instantly make a Spiritual Communion. (Thoughts of the Curé D'Ars, p. 35)
Of course, it is not God's love for us that grows cold, but our love for God. Or, it is our awareness of God's love for us that grows dim.
As Vinny Flynn points out in his CD on the Eucharist, spiritual communion is not a consolation prize when we can't receive Jesus sacramentally. Rather, spiritual communion is a way to keep sacramental communion a vital part of our daily lives.