Blogger comes with a Profile (or About Me) gadget. Your display image and a small description about yourself will be shown in this gadget. However, there are few drawbacks with this conventional gadget. Say you have two or more blogs. One for your family, and another one for your work. Your default profile gadget will be the same for both these blogs. You might not want that, as you might prefer to show different information about yourself on each blog. That's when Custom Profile comes to your rescue.
Another scenario. If you have a team blog, your Profile gadget will automatically turn into a contributors-list gadget. If you want to show individual profile gadget for all (or some) of your contributors, you can use this custom profile gadget. Best part of all, it's so easy to add.
On top of that, you can stylize this gadget as you want. With the default profile gadget, you have to settle for this pre-existing unalterable format. With a custom profile gadget, you can give colors to your text, change 'View My Complete Profile' line to something else, position the contents of your profile however you want, underline/bold/blink certain text, insert table in your profile (what?), add border around text, change display image size, and much much more! Your creativity is the limit.