During the Middle Ages, class was a very important factor for people. The class that you belonged to could determine a lot of situations in your life, including the type of job that you could have or the person that you could marry.
Kings and nobles were at the top of the social hierarchy. These people were very wealthy and they had a lot of opportunities in life. Afterwards, we would find the clergy, which included monks and nuns. As they lived in monasteries and received money from others, they also lived quite comfortably. Finally, at the very bottom we would find the peasants. Peasants were generally very poor and relied on very little to survive.
The people who could have beneffited the most from the idea of "Carpe Diem" would be the king and nobles. This is because such people had the most opportunities in life, and could therefore, reap the highest benefits when trying new things or chasing the things they desired.