With use of the Serialevent, it can be used to capture information received via the defined serial port, whilst the main programming loop is running allowing analog temperature readings be taken, LCD screen updates. However it is then up to the main processing loop to access the information received?
If I understood you right, it's not exactly like that.
The Arduino core code calls your setup() routine at start and then it calls your loop() routine in an endless loop. If some bytes were received during execution of the loop() routine, they were stored in an internal buffer. As soon as your loop() routine ends, the core code will call serialEvent() if it's defined and if there are bytes waiting in that internal buffer, before it will call your loop() routine again.
I hope that make this clear for you.