I've logged an incredible number of FF miles hauling back and forth to Florida. Delta gives 1000 each way. American figures actual miles of about 960. However if I can get a really cheap flight, I pass the opportunity to get miles.
I figure the miles are worth slightly less than 3 cents each.
I'd rather travel cheap and have the money in my pocket than get the miles.
Save some of your miles for those emergency trips when you have to haul out to see Mother in the hospital. If you have a miles award certificate in hand, you can go out to your airport and get a ticket for a flight. I telephone ahead to get a reservation.
Both American and Delta are very good about getting me on flights when I have to go in a hurry. Yes, I would prefer to use my miles to go to Europe, but it's cheaper to use an award certificate to get an emergency flight than to pay 'day of' prices.
Both American and Delta are very aware of family members that 'gotta go' to St. Pete in a hurry. The customer service reps at both airlines have always been wonderful.