At one time this was very true, and in some ways it can still be true. parts like the fans wear out, and due to the space constraints in a laptop this is more critical, and there are some thermal considerations to think about as well. but as long as you are giving decent airflow around the laptop, and you are prepared to swap a fan sooner than later it should have no real impact on the hardware.

I run mine for work 9+ hours straight and the previous one i had did this for 4.4 years before it finally got weird enough to be replaced.

I would most definitely enable power savings on your monitor because that screan can suffer from burnout, and its not as easy to replace as a monitor.