pointlessly

This adverb carries a strong negative connotation of futility and waste. It suggests not only a lack of purpose but often a sense of frustration or absurdity, implying that the effort expended was entirely devoid of value.

In terms of register, it is versatile and used in both casual conversation and formal writing. It is frequently used to criticize an action or a decision, contrasting with "purposelessly," which is more neutral and simply describes a lack of a specific goal.