Related: When Do My Miles Or Points Expire?
Redeeming miles is safer than the various methods of earning miles as point earnings don’t always post and it can turn into a fight in case your account expires. But as with everything else in life when you’re paying for something you can be sure that it will always post without any fighting required :D
There are actually get some pretty sweet deals, like The Economist for 3,200 miles. Delta miles don’t require activity, but still 3,200 Delta “Skypesos” for a year of The Economist isn’t bad at all!
Or you can just get a cheap magazine for 300-400 miles to keep your account active.
Alaska requires activity every 24 months.
Frontier requires activity every 18 months.
Hawaiian requires activity every 18 months.
Spirit requires activity every 3 months.