Question on impede information flow

Hi, Thanks for your great work
In section 3 in paper
"However, the identity function and the output of H_l are combined by summation, which may impede the information flow"
I did not understand that, there is also similiar question on stackoverflow
https://stackoverflow.com/questions/52696110/resnet-how-could-summation-impede-the-information-flow
Looking forward to your reply
