Story Points vs Time based estimations

Sooner or later you will be asked to make estimations in Story Points.

Don't.

Unless you exist in an isolated team with no collaboration or dependencies outside your own team, and you have your own budget, then story points will be completely useless. Even though story points are time allocations just like time based estimates, they have several drawbacks that make them less than ideal for estimation purposes.

1. Story points are arbitrary - This means that each team will have their own version of what a story point is. With no common point of reference it becomes impossible to use in situations where you work with accumulated data from multiple sources. Like portfolio management.
2. Story points are unflexible - This means that story points act as fixed size time slots with fixed ratios. That means that most estimates will either be a very snug fit or very loose fit. There is no one size fits all version in time estimations. That is for guestimations.
3. Story points are abstract and hard to understand - Since story points are made up of measurements that is also arbitrary, it is very hard to grasp what they mean for people working with time as focus for resource and finance planning.
4. Story points have no path of learning - This means that if you assign a value and you complete the work in that time slot, then you will never change that, even if the estimation was way too big. There is no proper learning curve as you either overestimate or underestimate and you either fail or succeed. You never learn by how much you over or underestimate as you never log more or less points.
5. Story points can't show progress - Story point can't be counted down like time based estimates. You only log start and completion, nothing in between. This can make for long periods of time before and update, which will make dependency management near impossible. Many reports will also be useless.

One of the most asked question about estimation with story point is how to translate to time. This is because story points does not work in most cases due to the fact that the rest of the world deal with time, not made up increments of arbitrary measurements.

So use always use time based measurements unless management tell you they need the estimates in that arbitrary measurement.