It is very common for people to use fertilizers in their garden.  Fertilizers contain nutrients that help to stimulate plant growth.  The purpose of planting a garden is to have plants that grow, so it only seems logical to fertilize your garden to promote that growth.  In some cases fertilizers do more harm then good, especially if you are using transplanted items. 

Using potted or containerized plants in your garden is very common.  These plants have already started growing, so you have a jump start on the plant when it is put in the ground.  Bareroot items are also popular.  They are often cheaper then containerized materials and in the case of on-line or mail ordering, you can sometimes find items that are not available in your local area.  In either case, people are integrating plants into their garden that began their growth somewhere else.  When this process takes place, it takes a little time of the plant to adjust to its new home.  Often the plant will show signs of stress or shock.  There are many examples of this.  Loosing leaves, the tips of the leaves curling, or the leaves loosing their green color are a few.  In the case of dormant bareroot items, it may just appears that there are now signs of life above the soil.  At this point, the plant should be re-establishing its root system.  

At this point, the plant is not growing.  The plant is using its energy to reset its foundation.  The issue with fertilizers is that they stimulate growth.  If the plant grows before the roots have been established, the roots will not be able to provide the nourishment needed for the new growth.  This can cause growth problems and in some cases it is fatal to the plant.  Generally, you want to wait until the plant has had a chance to become established before you fertilize.  Another idea is to use a slow degrading tablet (sometimes called a "pill") that will not promote rapid growth in the plant.  .