The resolution 1080p means the monitor has 1920x1080 pixels. Thats 2,073,600 total pixels your gpu has to light up with color.
The resolution 1440p means the monitor has 2560x1440 pixels. That's 3,686,400 total pixels your gpu has to light up with color.
1440p is @ 1.8x more pixels than 1080p, which is why it's often (incorrectly) referred to as 2k resolution.
What that translates to for a gpu is a seriously heavier workload. If you were getting 100fps in a game, expect to get closer to 60-70fps instead. With the same detail settings.
Comparing a 27" monitor with both resolutions, the 1440p will have considerably smaller pixels than 1080p, just to pack them in the same frame size, which results in a much cleaner, sharper image for everything from text to object edges. If you took a 1080p square with 10x10 pixels and drew a diagonal line, you'd see the stair-steps, not clean. Taking the same size box in 1440p, it'd be 18x18 pixels, far smaller stairs, much cleaner look.
So there are benefits to upgrading resolution, as far as viewing goes, but the downside is the huge draw on the gpu. Weaker gpus will tank for fps. If your gpu isn't 1080/2070S or better, 1440p will result in a bad time for fps when playing even simpler graphics games like CSGO.
1440p is to 720p the exact same thing as 4k is to 1080p. 2x2.