From Queness –Speed Up Web Page Loading By Deferring Javascript:
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Deferring JavaScript execution is an efficient approach to accelerate web page loading and improve user experience on reading. From the true experience, migrating our website to a Softlayer dedicated server (Xeon 3360 Quadcore 2.83GHz & 4GB RAM) from an economic VPS plan only speeds website up by 20%, but deferring JavaScript execution helps 50% increase, seeing in the Google Webmaster Tool > Site Performance.
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