Google Analytics is a web analytics service offered by Google that tracks and reports website traffic. It is the most widely used web analytics service on the web. Google Analytics provides an SDK that allows gathering usage data from iOS and Android app, known as Google Analytics for Mobile Apps.
Can Google Analytics slow down your Website? Any additional calls to scripts will slow down your site. However, Google Analytics instructs you to place it in a specific place so that it isn’t loaded until the page has loaded. It used to be before the body-tag but it’s now supposed to be the last script in the head-tag.
Straight from Google’s analytics: “The appearance of your website will never be affected by your use of Google Analytics – we don’t place any images or text on your pages. Likewise, the performance of your pages won’t be impacted, with the possible exception of the very first page-load after you have added the tracking code. This first pageview calls the JavaScript on Google’s servers, which may take slightly longer than a regular page load. Subsequent pageviews will use cached data and will not be affected.”
So don’t worry about it too much, because the benefits of analytics will far outweigh the extra call to a remote file. Focus on other optimizations (database queries, CSS sprites, fewer HTTP requests). Analytics is necessary in today’s site market and is indispensable; IMO it is not an option to forgo it.