Whether the boat sails better in certain conditions under just main or just
jib/genoa really depends on the boat, I suspect. Our Pearson P30, for example, sails very nicely on just the main, windward and all, reefed or not.
But our main comes down closer to the deck than that of many newer boats, which, I think, are rigged for more room above the boom for dodger, bimini, etc.
Admittedly, one reason we choose the main over the foresail is because, with a Tuff Luff system up front, the main is simply easier to hoist and stow
.
Jim