or Opera you will see an icon on the tab when you visit a page.This is called favicon. Favicon is a small icon/picture (usually 16px x 16px in size) shown next to site URL in the address bar. In Blogger, by default orange colored blogger icon is shown as favicon which looks ugly and it is common also as lakhs of blogger blogs contain this. Also having your own favicon with a nice graphical reminder of your site beside is a good way to attract visitors attention.
As you all know, Blogger has a new feature which allows you to change your blog's favicon without HTML coding (you still can use the codes if you want though)