It is always considered smart gambling when players give themselves a bankroll. A bankroll is not just the source of money to spin the reels of a slots game. It is also the limit to your playing. Smart slots players will stop playing the slots when their bankroll runs out.
But the problem then becomes how much money to bring in order to enjoy playing the slots. First you have to determine what will make you enjoy them. Usually after winning, which a bankroll cannot impact, is the amount of time played when determining whether or not slots are enjoyable.
So you need a bankroll to cover the amount of time you want to play.
Time is not as it appears to be when playing slots.
Time is not measured in minutes. It is measured in spins. You might spin the reels slower than the guy next you. In half an hour you might have played less and have retained more of your bankroll, leaving you more time to continue playing, than that guy next to you who spun the reels twice as fast and has less money left to keep playing.
Put another way, the faster you spin the reels of a slots game the faster you will play through your bankroll. And the actual time it takes you to play out your bankroll means nothing. It is the number of spins that measures the enjoyment and lifespan of your bankroll.
Spinning the reels less often in an hour will cause your bankroll to last longer.
Think of how much you want to spend on a spin. Say you are going for the longest possible life for your bankroll, and are only going to wager the minimum amount per payline, then a twenty payline slots game would cost you $0.25 per spin.
Now that you know that each spin is going to cost you a quarter you can begin to figure how many spins you can play, which will determine how long you can play. If you have a bankroll of $200, you can play for 800 spins.
Determining your bankroll is part of your slots strategy. It helps you to know how long you can play so that you do not spend more than you know you should.