Acting on physical desire could symbolize taking advantage of one's youth and passions in myriad ways. Most literally, in the poem, the speaker encourages his standoffish beloved to sleep with him now because time passes so quickly and life is so short. However, acting on this physical desire might figuratively signify acting on any kind of dream or wish while we are young. In our youth, we are often nimble and blithe, energetic and passionate, and we have lots of dreams and hopes. It is during this time that those dreams and plans seem most within our grasp, and the poem's insistence on taking advantage of one's youth could apply to these as well.
Further, the idea that death comes to us sooner than we think it will is pertinent to this symbolism as well. We should waste no time in pursuing anything that we truly desire, because time is so fleeting and swift-moving. In waiting to pursue the things that we want, we only tempt fate and risk dying before we achieve them. The speaker talks about what a waste his beloved's virginity would be in death and how her "quaint honour" then will matter not at all to the worms. Similarly, what a waste of our time and potential as human beings if we die never having taken risks or really gone after our dreams.