Depending on the monitor screen size you will see little to no difference. For example. 24 inch and lower size, I do not think you will ever notice the difference. 1440p and 1080p, or 2560x1440 and 1920x1080 is the number of pixels (width times height) you see on the screen thus when going down from 1440p to 1080p you will see less pixels thus the image is less sharp and if you have a big screen you will be able to see those pixels at a certain distance.
Hope that answers your question.