With Google focusing on site speed as a ranking indication for SEO, we get this question a lot. Folks are worried about things that slow their sites down and so they want to make sure that Hello Bar won't pressing the brake pedal.
Every plugin that you add to your site has some effect on your site speed. For instance, Google Analytics slows your site down in a microscopic (and inconsequential) way. A chat feature slows your site down a bit more, but still is pretty harmless. Certain ad units, have a larger effect and will slow your site down in a pretty measurable way. If your site's images aren't optimized, then they can really slow your site down. But, though Hello Bar utilizes javascript to function, it's effect on your site is typically imperceptible, closely aligning with the load time of (or sometimes faster than) Google Analytics.
Using the Google site speed tool, we got some numbers to help put things into perspective.
Here is the load time from our own website, that a popular web chat tool ads to it:
(About 1,300 ms or a little over 1 second)
Here's Facebook Connect:
(about 196 ms or almost 0.2 seconds)
Google Analytics takes:
(102 mx or about 0.1 second)
And finally, Hello Bar adds:
(112 or about 0.1 second - almost the same as GA)
SUMMARY:
While all plugins and additions to your site add something to it's load time, some are negligible in their effect. 0.1 seconds in this case, is not going to be perceptible to any human visitors nor will it hurt you with Google's non-human visitors.