When the visitors land on your site, they are very much ready to even exit your site, unless you convince them in 3 seconds that it is the place where they have to be. It does make an immediate impact.
In those 3 seconds, you need to indicate key elements like who you are and what you do within those 3 seconds.
Who you are
Your company logo represents you. So it needs to be designed well as it holds the identity of your company. Most importantly, it needs to be placed on the prominent place so that it is the first thing that people see after they land on your page.