understanding usart code

void main()
{
while ((UCSRA & (1 << UDRE)) == 0) {}; // Do nothing until UDR is ready for more data to be written to it 
UDR = ByteToSend; // Send out the byte value in the variable "ByteToSend"
//bellow is the code of main program
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}

UDR = ByteToSend; // Send out the byte value in the variable "ByteToSend" 
while ((UCSRA & (1 << TXC)) == 0) {}; // Do nothing until transmission complete flag set

while ((UCSRA & (1 << UDRE)) == 0) {};

main(){

while(1){                                                //start of never-ending loop

while ((UCSRA & (1 << UDRE)) == 0) {};      // every time the program returns to this line, it determines if transmission is 
                                                           //already done. the 1 second required may already have elapsed and you no longer have to do any more waiting.  
UDR = ByteToSend;                                 // Send out the byte value in the variable "ByteToSend"
                                                            
//rest of the loop. notice that there is no 'waiting' done after the transmit instruction
 the program continues [I]while[/I] the byte is being transmitted, so while 
the 1 second required is ellapsing, other instructions can be carried performed. if this part takes longer than 1 second, than you can
be sure that by the time you return to the beginning of the loop, the usart module will be ready for transmission again and you no longer have to wait
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//


} //return to beginning of the loop. 

}

main(){


while(1){                                                //start of never-ending loop

UDR = ByteToSend; // Send out the byte value in the variable "ByteToSend"
while ((UCSRA & (1 << TXC)) == 0) {}; // Do nothing until transmission complete flag set. everytime the loop
					//returns to this line, you will always have to wait until after tranmission
//is complete before proceeding. this is why it is less efficient than code #2 

//bellow is the rest of the loop

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} //return to beginning of loop

}