It's up to you. But my opinion is to update all apps regularly. Because updating apps helps in battery optimization,memory and performance.
1.Battery Optimization: There's a reason developers constantly update apps, and most of the time it's memory or battery optimization. Keeping your apps updated also means you have the best optimizations available. Likewise, delete old apps you no longer use, because these may be running background processes that chew up RAM and battery life.
2.Memory: The updated apps generally use memory efficiently in most of cases, though I don't think there would be much impact due to it. You can clear the caches or use softwares like 360 Security or Turbo Cleaner for that purpose.
3.Performance: Not always, but most of the time there is a improvement.