You don’t have to restart your device to speed it up and fix memory issues
Have you noticed your iPhone slowing down at all since its last update? If it's slow to respond, crashing, or freezing on random screens, it may be a problem with the device's memory.
Although the iPhone's RAM automatically clears when you restart the device, you don't have to reboot it in order to speed it up and fix these memory issues. If you have an iPhone 4 or later model, simply follow the steps below to refresh your iPhone's memory without rebooting it.
- Unlock the iPhone.
- Press the Sleep/Wake button until a screen appears telling you to Slide to power off. There will be a Cancel button at the bottom of this screen.
- Release the Sleep/Wake button.
- Press and hold down the Home button until the phone returns to your Home screen.
- Release the Home button.
- If it continues to crash, restart it completely by holding down the Sleep/Wake button and sliding to turn it off, then press and hold the Sleep/Wake button to turn it back on.
Source: iPhoneLife Magazine