A laxative acts faster.
Osmotic laxatives (which brings water into the system), stimulant laxatives (which makes gut muscles work harder), emollient laxatives (makes your poop slippery) all offer relief from constipation by encouraging waste to leave the system.
Too many laxatives, though, create dependence and often lead to loss of gut muscle tone.
Said differently – a laxative is a quick-fix, not a long-term solution.