Do we have to perform shraadh? If we don't perform this ritual, will the future generations suffer?
No, don't be afraid. Shraadh is a ritual performed in the memory of people who have passed away. In their memory, you do some good work, feed a few people - that is what it is. Even the mantras that are chanted during shraadh say, "My father, my grandfather, and great grandfather, all three of you, come, I am serving some food to you with devotion, please accept it". This is all that is said in the mantras. It is spoken in Sanskrit, it could have been said in Hindi too; that is all.
It is a ritual that has been going on for generations. Shraadh means doing something with devotion, i.e., shraddha, it is doing some good deed for people with devotion.
In the olden days, when they realized that a person has taken rebirth, they would cease with the ritual. Now, people don't know whether the person has taken rebirth or not, so they keep on performing shraadh.