Weather
In the NFL, the only time a game is called off due to weather is when there is lightning, or in extreme circumstances (the New Orleans Saints couldn't play soon after Hurricane Katrina). Many teams need to adapt to play in high temperatures, and others in snowy conditions. This may sound easier than it is as players are brought into teams from every part of the US. When the Arizona Cardinals hosted the Green Bay Packers in 2003 they played in 41 degrees Celsius. The Cardinals won 20-13, a sign of experience of playing in high heat.
Routine
As with every sport, players have a much easier routine without travelling disrupting their schedule. Many plane trips can disrupt a player's sleeping pattern, meaning they are not 100% for their games.
Arizona Cardinals Stadium