Sampat Path takes a lot more time than Akhand Paath Sahibs. In sampat paths, usually a shabad is picked (could be at random, or one could be picked to serve a specific purpose) and then it's read after the ending of each shabad in Guru Granth Sahib Ji.
Sampat Paths are of two types, u can either do it like a sehaj paath, or like Akhand Paath.
I'm not sure how old is the idea of having sampat paaths but many jathebandis believe in holding them.