Those tactics are more for fear effect. Romans didn't have tons of complex formations like some could believe. Basically, imagine columns of soldiers fighting beside each other, sometimes swapping place with the guy behind so they can rest.

Behind the main battle line, the other units are in a checkered formation because it offered great mobility and ease for changing the men in the front for fresh troops.

Romans did also break formation, for example when being flanked. Or while attacking a smaller unit, they would break formation in order to surround the ennemies.