While practice of any kind will help you reach a higher level, like it or not, drills are particularly helpful because:
1) They provide good practice without the pressure of a game, and
2) Whatever your level, you’ll get more practice in the same amount of time when concentrating on just one thing at a time.
Some players have a weekly regimen of drills they do to keep them on top of their game. Some work strictly on elements that need improvement. Some split their time doing both.
I believe drills are best used to focus on what you do poorly to make that your strength. Maybe you always miss your drop shot, or lobs always go long. You know what your problem areas are—but you probably don’t know what you’re doing incorrectly that causes the problems or what to do to fix them. (If you did, you wouldn’t still be making the error!)