If you look at the void loop you’ll see that it only executes once, as the last line of the void loop puts the device to sleep. That code could be in void setup and have an empty void loop and it would work exactly the same way.
The ESP8266 code has actually moved-on quite a bit since the version that @christophebl has posted here, as he realised that Blynk.begin was causing problems if the device wasn’t able to connect to Wi-Fi, or Blynk, for any reason. The ESP was constantly trying to connect and draining his battery because it was never going to sleep.
We made some changes to use Blynk.connect instead, and limit the number of Wi-Fi connection attempts and added some logic that allowed a different sleep duration after a failed connection attempt.
Pete.