Google Play accepts screenshots in specific dimensions. Phone screenshots are often 1080×1920 or 1440×2560; 7" and 10" tablets have their own min/max dimensions. Providing correctly sized images keeps your listing professional and avoids scaling artifacts.
Minimum and maximum
Google has minimum (and sometimes maximum) dimensions per device type. Too small and quality suffers; wrong aspect ratio can cause letterboxing. Use a resizer that targets the official Google Play screenshot sizes so you're always within guidelines.
Multiple screenshots
You can upload several screenshots; the first is often used as the feature graphic in some contexts. Resize all of them to the required dimensions in one batch with a tool that supports multiple images and outputs a ZIP.