I don't see either point. You don't want your benchmarks to interact, and normally have to make sure they don't. Forking saves you that trouble. That also means yellow flags should be raised only if you wanted to use the non-forking benchmark as the baseline — but why? Sure, if you find differences and didn't expect any, it's worth investigating the source of the interaction — if it's not in your own benchmarked code, modules you pull in might have an issue you weren't aware of. But beyond that, provided with a means to entirely isolate benchmarks, I just don't see any reason to go to the trouble to make them "clean".

In the example given, there are two possible scenarios.

1) The intention is to test how each version of a piece of code handles a specific problem. In this case, you're exactly right.

2) The intention is to test how each piece of code is performing in a larger prog. In this case, both the performance of the individual segments and the interactions among those segments in the real-world case are valuable, so you want both the 'isolated' and 'non-isolated' cases.

In any event, I like the module. In case 1, it allows for testing of several very similar segments of code non-interactively at once, regardless of whether the coder knows they would otherwise be interactive. (Another goot habit, like 'use strict'.)