This is about bankroll management. By increasing your bet size and lower your number of bets you increase the variance. If you are on average a negative EV bettor, this doesn't not matter to you because overtime you will reach $0.
Generally speaking when you factor rollover into consideration you want to increase the betsize and lower the number of bets. Because when you factor in, busting out zeroes out the rollover and you can redeposit for more bonus (BOL, SB.AG, BAS, Bookmaker...) there is inherent value to busting out to clear the rollover.
But I think 98% of bettors are in the negative EV bettors so it does not matter. Overtime they will reach $0.