Two modes are available to insert a sequence from the original track to an edited track.
Replace mode : "simple" insertion without moving a sequence. It means that the insertion will be done only if the space is enough.
Insertion mode : when you click on "replace mode", you go to the "insertion mode" function.
This function enables you to insert a sequence by moving the other ones if you do not have space enough.
Moreover, this function enables you to stick down all sequences in case of splitting a sequence (to keep the same space between the different sequences for instance).