As an adjective, 干脆 means 'straightforward, direct to the point' with a sense of decisiveness — it's more emphatic than 直接 (zhíjiē), which simply means 'direct' in a neutral or literal way. As an adverb, it means 'simply; might as well; just (do something)', used for a decisive suggestion or action; it's stronger than 不妨 (bùfáng 'no harm in'), and very close to 索性 (suǒxìng) but slightly less focused on a change of plan.