I often read that it is good practice to connect VCC with AVCC. Even in the ATMega8 datasheet it says so:
AVCC is the supply voltage pin for the A/D Converter, Port C (3..0), and ADC (7..6). It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter. Note that Port C (5..4) use digital supply voltage, VCC.
But nowhere I can find an explanation as to why they have to be connected. A simple circuit for blinking a LED works without connecting VCC and AVCC.
Do I just have to accept it, or is there a good reason?