If you have to check bags, there is a cut-off time. If you arrive too late (traffic jam, breakdown, whatever) you're not allowed to check bags
there is another cut-off time after which you're not allowed to board the plane at all
it sometimes ranges from 45 to 90 minutes, depending on destination, airlines and airports.
That's not a chance I'm willing to take.
Time needed at the airport is impredictable. But there is one thing, derived from Murphy's law :
If you're there early, it will move fast and you'll have too much time to kill at your gate and you'll swear that next time you'll sleep in a bit more ...
But, if you're there later, all lines will be frozen to a stand still for ages, and you'll barely make it for your flight
(you know, it's like the line at the check out in your local supermarket. The next line moves faster than yours ... until you change lines, and that's when that line's register suddendly stops working, or each customer pays with 1p coins)
at the end of the day, it's always best to sit for 1 hour at the gate because you came in too early, than sit for 24 hours at the gate because you missed your flight
2.5 hours is my bare minimum before a flight with an international connection
A last burger at the food court is also a family tradition for us (usually it's a wendy's airside, but this year will fly out of the other terminal ... well, we'll make do

)