Story points...
Abstract Complexity, Not Time:
Story points measure the relative complexity of a task or user story rather than the absolute time it takes to complete. This abstraction allows teams to focus on the effort required to deliver a feature rather than getting bogged down in estimating hours or days, which can be highly variable and affected by external factors. Time is also heavily based on WHO is going to do the work. This can add another level of variable which can throw off the expectation for a sprint. If the individual who was “SUPPOSED” to work on the story is now no longer available, you MAY NOT have another individual as skilled to complete the work which risks a delay, or the work being deferred to another sprint.
Promote Relative Sizing: