...because it gets around the max bet rule
If the max bet is $6.25, you can reduce the number of lines to 6, betting $1 on each. When you do hit the bonus, your free spins are on a $25 bet, which would be against the max bet rule were it triggered with $1 bet on all lines. You could even bet $5 on one line, and have your bonus round playing out at $125 per spin.
This sharply increases the variance in the same way that placing very big bets does.
This game will probably be banned for bonus play, or set to a compulsory max lines like the "feature guarantee" series of slots.
Because free spins play at max lines, your retrigger chances are not reduced by playing fewer lines, even though your chance of initial triggering is sharply reduced. It is a great strategy for beating the $150 for $500 bonus It will fail nearly all the time, but when you hit, it could be VERY big. It should be used with great care where a max cashout is in force.
I see. I was hoping for something better that actually affects RTP and not just variance. Playing fewer than max lines increases the variance on any slot, not just Fruit Frenzy. In fact in the previous slot mathematics thread I gave some numerical values of how much the variance increases as a function of reduced lines (assuming total bet stays constant). It certainly is a useful play when you get a large % bonus and your max. allowed bet size is restricted. 32Red SUB has similar bet size restriction and playing fewer than max lines there might be a good idea as well.