You don't really "see" pixels on a LCD screen, what matters is the sharpness of your image because if there are less pixels on 1 cm², the pixels become bigger and theres less color variety.
For example on a 16:9 ratio with 24" you get w53xh30 = 1588cm².
On a 16:9 ratio with 27" you get w60xh34 = 2010cm².
1920*1080 = 2073600 pixels
So ~1306 pixels/cm² on 24" and ~1032 pixels/cm² on 27".
That makes quite a big difference in image sharpness and color variety.
If you pump up the resolution to 2560 x 1440 you get 3686400 pixels or 1834 pixels/cm² on 16:9 @ 27", theoretically resulting in a much sharper image than 1920x1080 on 24" 16:9.