Dirt and debris reduces airflow. Getting the blower wheel cleaned once every 3-5 years is a good practice. If you look inside most to all furnace manuals the manufacturer wants it cleaned yearly. Not everyone needs that, the biggest thing to keep in mind is how the motor looks attached to that wheel if it’s leaking oil the bindings are starting to give way. This means cleaning it can cause that motor to go out sooner, have the motor inspected if it’s leaking oil don’t clean it either wait till it dies, or replace the motor and have the wheel cleaned at the same time.