By definition, you would not have to use floating ability scores. They would start out as the default, and you could choose to swap them, or leave the ASI's where they were. It would not affect you, but it would allow for say, a Halfling Wizard to exist without being mechanically penalized. That would allow more players to play how they want while not affecting players who wanted to keep the default.
Is a halfling wizard actually penalized though?
Lucky trait is amazing. It's worse than +1 to attack rolls, but not by much. Not to mention ability, saving throw checks, concentration. And you should have either +1 to dex or +1 to con compared to high elves or humans.
You lose 1 DC on your spells that's for sure, but your constitution score should be higher so concentration benefits.
And most importantly in 5e you can build your halfling wizard around the notion that you have lower intelligence to an extent that was not possible in previous editions. The amount of excellent spells that don't care about your int is astounding. And if you do focus on those spells a dwarf (due to proficiencies) or halfing are better choices than +int races.
Racial ability scores breed creativity while floating stat bonuses discourage it.
