On winning the coin flip you get dibs of 4 choices: receive, kick, defend a goal, or defer your preference to the second half.
Generally the winner will defer because it's advantageous to have your choice in the 2nd half. Then the losing team has dibs and will usually take the ball for first possession.
I vaguely recall one of those Witch Of November games in the 90's at the Rich against the Cardinals and if my memory serves Marv Levy opted to get the wind in the 2nd and 4th quarters, and kelly went bombs away with the wind and it was a complete rout.
Yep, wayback machine has it: November 11 1990, Bills 45 Cardinals 14. ALL of the scoring in the game came in the direction with the wind. The Bills had the ball in the 2nd and 4th and ran roughshod.
This is the one thing Allen hasn't mastered yet is how to gauge the wind in the home stadium. Kelly would lob the ball up as if it was a 30 yard throw knowing it was going to travel 50, and it did.