Should you pay extra for an airline seat assignment?

Here's the answer. Warning: You might not like it.

Is it worth paying extra for a seat assignment on a flight?

For Donna Shelton, the answer is: almost never.

"OK, I just made an exception on a flight from Houston to Chicago," says Shelton, a banker from Chicago. "I brought home a stray cat I had rescued while visiting my family. I wanted more legroom to access her carrier, if necessary."

She reluctantly f…