I'm looking for advice about favicons and their impacts on search engines. Recently I noticed a site which changes its favicon every time you load another page without losing overall recognition of the favicon style. I'd like to incorporate this into my site as well but am I taking any SEO risks here?
The favicon CAN have an effect on SEO. I saw one case where a website had a favicon that was about 400kb in size - slowing the website down. Speed is a Google ranking factor and slow loading sites likely have poor metrics, which can also negatively affect SEO.
Also, most browsers automatically look for a file called favicon.ico in the root folder of a website - if the file doesn't exist a 404 Not Found error is returned - so it makes sense to have a small or blank file rather than nothing to prevent that extra server hog.
If you have a different favicon on each page, make sure to keep the file size as small as possible, to minimise the impact on download speeds.
I think favicon.ico helps. Search Engine bots will think that you customize your site and brand it well by putting its own icon. Another thing some social network sites are using your favicon to display preview of your site.
Spamblogs and Made for ads sites doesn't care about favicon or to effort to create a website logo. My two cents.
Source: my SEO experience