I fill everything out and still wait until the clerk asks before deciding on Power Play. Half the time I say yes just because the question caught me. I need one rule for myself. Do you add it every time, never, or only at certain jackpot sizes?
On a US Powerball play, Power Play costs an extra $1. The drawn multiplier makes most non-jackpot prizes 2, 3, 4, 5 or 10 times larger. Match 5 does not use the drawn multiplier; with Power Play it is fixed at $2 million. The jackpot is never multiplied.
The 10X value is only available when the advertised jackpot is $150 million or less. Power Play changes the prize table, not the numbers or jackpot odds, so the sensible personal rule is whether the extra cost fits the same entertainment budget.