Software testing concepts help us compartmentalize the complexity that we face in testing software. Breaking the testing domain into various areas (such as usability testing, performance testing, functional testing, etc.) helps us organize and focus our efforts.
But those concepts are constructs that often have fuzzy boundries. What matters isn't where we should place certain software testing efforts. What matters is helping create software that users find worthwhile and hopeful enjoyable.
One of the frustration I have faced in using internet based software in the last few years is that it often seems to be tested without considering that some users will not have fiber connections (and might have high latency connections). I am not certain latency (combined maybe with lower bandwidth) is the issue but I have often found websites either actually physically unusable or mentally unusable (it is way too frustrating to use).
It might be the user experience I face (on the poorly performing sites) is as bad for all users, but my guess is it is a decent user experience on the fiber connections that the managers have when they decide this is an OK solution. It is a usbility issue but it is also a performance issue in my opinion.
It is certainly possible to test performance results on powerful laptops with great internet connections and get good performance results for web applications that will provide bad performance results on smart phones via wifi or less than ideal cell connections. This failure to understand the real user conditions is a significant problem and an area of testing that should be improved.
I consider this an interaction between performance testing and user-experience testing (I use "user-experience" to distinguish it from "usability testing", since I can test aspects of the user experience without users testing the software). The page may load in under 1 second on a laptop with a fiber connection but that isn't the only measure of performance. What about your users that are connecting via a wifi connection with high latency? What if the performance in that case is that it takes 8 seconds to load and your various interactive features either barely work or won't work at all given the high latency.
In some cases ignoring the performance for some users may be OK. But if you care about a system that delivers fast load times to users you need to consider the performance not just for a subset of users but consider how it performs for users overall. The extent you will prioritize various use cases will depend on your specific situation.
I have a large bias for keeping the basic experience very good for all users. If I add fancy features that are useful I do not like to accept meaningful degradation to any user's experience - graceful degradation is very important to me. That is less important to many of sites that I use, unfortunately. What priority you place on it is a decision that impacts your software development and software testing process.
Hexawise attempts to add features that are useful while at the same time paying close attention to making sure we don't make things worse for users that don't care about the new feature. Making sure the interface remains clear and easy to use is very important to us. It is also a challenge when you have powerful and fairly complex software to keep the usability high. It is very easy to slip and degrade the users experience. Sean Johnson does a great job making sure we avoid doing that.
Maintaining the responsiveness of Hexawise is a huge effort on our part given the heavy computation required in generating tests in large test case scenarios.
You also have to realize where you cannot be all things to all people. Using Hexawise on a smart phone is just not going to be a great experience. Hexawise is just not suited to that use case at all and therefore we wouldn't test such a use case.
For important performance characteristics it may well be that you should create a separate Hexawise test plan to test the performance under server different conditions (relating to latency, bandwidth and perhaps phone operating system). It could be done within a test plan it just seems to me more likely separate test plans would be more effective most of the time. It may well be that you have the primary test plan to cover many functional aspects and have a much smaller test plan just to check that several things work fine in a high latency and smart phone use case).
Within that plan you may well want to test out various parameter values for certain parameters operating system iOS Android 7 Android 6 Android 5
Of course, what should be tested depends on the software being tested. If none of the items above matter in your case they shouldn't be used. If you are concerned about a large user base you may well be concerned about performance on various Android versions since the upgrade cycle to new versions is so slow (while most iOS users are on the latest version fairly quickly).
If latency has a big impact on performance then including a parameter on latency would be worthwhile and testing various parameter values for it could be sensible (maybe high, medium and low). And the same with testing various levels of bandwidth (again, depending on your situation).
My view is always very user focused so the way I naturally think is relating pretty much everything I do to how it impacts the end user's experience.