When a user accesses your site or blog, then they do not want to sit all day for your site to open.
It is really frustrating to sit and sit and sit and sit and sit...................... till the entire site is open.
If your site takes time then it may turn to loss in traffic. So how do you know how slow is your site.
Try this http://www.pagespeed.googlelabs.com
This is Page Speed Online by Google™. It tells you in percentage how slow is your site (100% being the fastest and 0% being you know).
And for your information, this blog scored a 89 out of 100.
So go now and try it.