More specific? Sure.

It's all in the big O. Suppose that your code runs OK when you have 1000 data points, how long do you expect it to take when it processes a sample of 50,000 data points? 50 times as long, or 2500 times as long? The latter can cause very nasty surprises. For an extreme example, if this code is being used somewhere that you have constant requests coming in (eg a website), as soon as the time to respond goes over the time between requests, your system will fall over. Been there, done that, not fun.

Therefore I'm careless of micro-optimizations until there is a proven problem, but I tend to stay much more aware of algorithmic efficiency issues.

As for whether it is useful to make quick comments about a module, what I'm really trying to communicate is that this is how I evaluate unknown modules. I sanity check them, and if there a significant red flag comes up, I won't use them in serious work. I do this because I think that it is a good practice. Because I think that it is a good practice, I think that there is value in encouraging other people to think about how they handle this. Certainly much more value than the common refrain of saying, It's on CPAN, use it!