Sometimes it is necessary to calm a nervous animal whether to examine him/her or to perform a minor procedure. This usually involves giving an injection or an oral medication a short time before the effect is desired. Many animals are simply nervous of the different surroundings in the clinic or do not like certain things being done to them (like having their nails trimmed). When they are relaxed they seem to tolerate procedures better.
Tranquilization is also sometimes given at home just before a stressful incident like a thunderstorm or prior to travel to reduce anxiety.