Other mistake: Captain Casey has Lieutenant pins on his uniform instead of Captain pins. (00:31:00)
Other mistake: In the pilot, Heather Darden states that Andy had been at the house for 14 years. Assuming that he was placed there directly after the Academy that would place his age at 32 years old at the time of his death (2012). In Season 3 (I Am the Apocalypse), April Sexton gives her year of birth as 1982, making her 33 years old in 2015. April and Andy both are said to be the same age as Kelly Severide, as Darden went to kindergarten with him and April sat next to them in class, however there is at least a 3 year age difference between Andy and April.
Answer: Internet sources give many reasons why firefighters do this, but in regards to your question, it's probably because opening walls and ceilings creates better ventilation which allows heat and smoke to escape, giving firefighters better visibility and lowering the temperature.
raywest ★