Running specs/tests involves reloading the environment for most people. Spring is surprisingly good for this, but you can still run into weirdness where spring needs to be reloaded due to some sort of state issue.
exactly. Rspec/rails is my favorite vim plugin but I really hate the time I spend waiting for the spec to run after I've typed \s (note: that's the actual key sequence not an indication that I'm being sarcastic).