It depends what you're building. In general, buying a 16 then adding a +2 racial bonus isn't prohibitively expensive, and still allows you to do a lot with your remaining points. So if you can, you might as well.
But there are some race/class combinations that work well but haven't got +2 racial bonuses to the attack stats. Like dwarf or elf fighters. Or if you're doing a "two attack stat" character, you might go with a 16 or 17 in both attack stats (half elf star pact warlock, 17 in con and cha, for example).
So, it depends? An 18 primary attack stat is nice in comparison to a 16, but its not vital to your character's survival and excellence, and if you have a good reason not to go for the 18, your character will still be competent.
But there are some race/class combinations that work well but haven't got +2 racial bonuses to the attack stats. Like dwarf or elf fighters. Or if you're doing a "two attack stat" character, you might go with a 16 or 17 in both attack stats (half elf star pact warlock, 17 in con and cha, for example).
So, it depends? An 18 primary attack stat is nice in comparison to a 16, but its not vital to your character's survival and excellence, and if you have a good reason not to go for the 18, your character will still be competent.