The usage of time point features

First of all, thank you for sharing your excellent work. I have a question regarding the use of the time point features: time_point_features = self.transformer(x) in line 42 of this file: https://github.com/MUYang99/MPTSNet/blob/main/model/MPTSNet.py 
Could you please clarify why this step is necessary, considering that it incurs a significant computational cost?
Thank you