Okay, lets show everyone how great your game looks! Open your Unity Project and press "Print Screen" until you're satisfied and that's that! What else could you do to improve your screenshots?
Then Say you'd like to add some effects, texts or just anything else to your screenshot in your favorite image-editing progra? No problems! You import your screenshots and after editing, exports them everything is fine and dandy!
But what's the problem then?
In my case this wasn't enough, and the problem started when I wanted to take a screenshot of my mobile game in the resolution of 1080x1920. My monitor's resolution is 2560 x 1080, and when taking a screenshot the upper half of pixels is almost gone since my monitor can only capture 1080 pixels in height. There is another way to solve this, which is to just take the screenshot on directly on a mobile device, but then you're limited to the device's resolution instead.
What I'm getting at is what if you would like to take a 4k screenshot with your 1080p monitor? With this kind of resolution you could also edit it and export it in a lower resolution to make your game look sharper and less pixelated.
The solution I found was the Instant Screenshot extenstion. A free and simple plugin for taking really big screenshots of your game. Playing around this extention, I was able to take screenshots far larger than 1080p and 4k! Even larger thank 8k (7680 × 4320 pixels)!
The result is speaking for itself.
Here is a simple screenshot taken from unity together with a zoomed-in section.
Here is the same frame of the game, but captured with the extension.