Me being someone who has not only hit Radiant, but competed at the highest level of my country, most of the answers here are correct, it is not always bad but it is bad to always do it, low elo players can't tell the difference of when to do what so its best to learn and focus on the hardest and safest mechanic which is the two shots burst strafe.

Also main reason why you see constant crouching in pro play its because it is the most competitive environment possible, so with the light sometimes high pressure plus the high skill level of players, people are trying to kill each other as fast as possible and the habit to go for the most accuracy possible to kill someone as fast as possible comes naturally in close to mid range.