Of course small/medium/large mean something, they are an approximation of size/dimensions. But story points, adherents claim, are not a measure of time at all! They are not "an approximation of time", they are, so it is claimed, supposed to be unrelated to time, but to "complexity".
And while I agree that a task can be large either because you know what must be done and there is a lot of work or because you're not sure what needs to be done yet. But conflating those two things as "8 points" or whatever is just not helpful.
Story points are also "an approximation of size/dimensions." If my team has consistently deployed 25-35 story points per sprint for the last three sprints, it's reasonable for me to assume that next sprint they will also be able to complete about 30 story points of work. By contrast, knowing that they worked a combined total of 300 hours on average doesn't help me at all. And accounting for uncertainty is important, which is one reason a Fibonacci sequence is commonly used. The general rule is to go up one in the sequence if the team is uncertain. The whole purpose of story points is to avoid having to track things like uncertainty separately. It's like the Markov assumption, the information to get to the current point estimate is baked in. It is useful (essential, even) to incorporate fuzzy concepts like perceived complexity or uncertainty without bogging the team down trying to measure them precisely and explicitly.
> If my team has consistently deployed 25-35 story points per sprint for the last three sprints, it's reasonable for me to assume that next sprint they will also be able to complete about 30 story points of work.
And if the last few sprints they've completed between 5 and 30 points, do you believe they'll complete around 17.5 points next sprint?
Now, if the team is good at estimating (which they are if they get consistent results between sprints), they can tell you of them telling you feature X is 8 points, Y is 5 points, Z is 15 points, and you concluding that they will finish X, Y, and Z next sprint. But, they can exactly as well tell you that X will take around 3 days, Y will take around 2 days, and Z will take around 5 days, and you can have the same conclusion.
>And if the last few sprints they've completed between 5 and 30 points, do you believe they'll complete around 17.5 points next sprint?
I don't know, what did the team figure out in retro? Was the big difference a real underestimation, or was there some kind of unforeseen blocker? I've never seen that big a variation, but anything's possible.
If it makes you feel better to measure team velocity in something you call "days" instead of story points and it works for your team, more power to you. But don't fool yourself that you're talking about actual days. At best you're talking about "probable days", and how many days it actually takes will depend on a lot of things, including unknowns and who takes the story (are "Bob-days" the same as "Carol-days"?). So you'll end up with a measure of days that is very team- and uncertainty-dependent, and at that point it's better to just use story points and admit that it's not a universal measure and doesn't need to be. Not to mention that by using days you'll invite confusion between calendar time and time-on-task.
And while I agree that a task can be large either because you know what must be done and there is a lot of work or because you're not sure what needs to be done yet. But conflating those two things as "8 points" or whatever is just not helpful.