What does it mean On-page Optimization ??

[PK357]

Because the code loads in a sequential order. In other words the script is read from header to footer. You want the GA snippet to get read right away so you can log every single visit to your site. If the code is placed in the footer or a sidebar widget and your page takes a long time to load due to heavy code, rich text/images, people can close the browser and bounce before the code even renders.

That means you haven't even logged the visit. If this happens a lot, you think you have less visitors than the actual number and also, your bounce rate is much lower than actual number. So you are getting improper data each month. Google analytics data is used to optimize your site, but if you have incomplete data or incorrect data you won't do a very good job of making on-page optimization changes. In this case, long load time is negatively affecting your SEO, but you won't know it because your bounce rate is lower in GA.

It is an easy thing to remember so always do it.

Also, use the header.php because php includes, so you won't have to tag every single page.