@AVINASHL4108 Hi, This is my uderstanding. Abstrat class is very useful, when there is no need to store data.
Example : If you are connecting to an REST Integration, you will get data from external systems. Hence you need not store data in Pega ( as you are not owner of data too), you can refer/get data from integration systems . So, in this case, you can define integration classess as abstract classess.
Also, apart from this, there are some times, you need properties in pega just to hold data in work object and you dont want them to store internally in pega table. So, in this situation you can use abstract class.