We’ve done it: forgotten to soften the butter and zapped it in the microwave to do the job quickly. Better to let it stand at room temperature for 30 to 45 minutes to get the right consistency. You can speed the process significantly by cutting butter into tablespoon-sized portions and letting it stand at room temperature.
Properly softened butter should yield slightly to gentle pressure. Too-soft butter means your cookie dough will be more like batter, and it will spread too much as it bakes and lose shape. Butter that’s too soft also won’t cream properly with sugar, and creaming is essential to creating fluffy, tender cakes with a delicate crumb.