As muchmass says, if you can fit it in your diet, go for it. But at some point the further you take your cut, bananas may not be your best choice as they are higher in sugar and don't have the thermogenic to carbohydrate ratio that something like blueberries would have.
This becomes an issue only as calories become a premiun...that is when bodyfat gets low and you only have "X" amount of calories to play with, and you still want fruit, then a banana may not be the best way to go.