#1. In terms of Monetization: Many Big Advertising-Publishing Companies such as "buysellads" Do Not Accept Blogs with subdomains because they feel that blogs with sub domains might bring down their Reputation.
#2. Easy To Remember: Yes. Custom Domains Are easy to remember in the sense that it is easier for you blog readers/subscribers to remember you blog on custom domain than when it is under a subdomain. Take for instance,you have a subdomain as www.etechville.blogspot.com and a custom domain as www.etechvilla.com, check it.. Which would be easier for you to remember?? This is on good advantage.
#3. Incase Blogger Deletes Your Blog: This Is One of the Major Disadvantage of Blogger.. Your Blog can be deleted any moment. Having a Custom Domain, it doent mean that your blog cant be deleted but you can Move to another blog within a few hours even though it wont be easy to get back your contents, your traffic, Page Rank, alexa rank etc will remain constant.
#4. Search Engine Ranking: A Custom domained Blog has a higher opportunity of ranking on Search engines. Even though the difference is Not Big, It can be proved by taking the example of top ranking sites for any keyword, you will find more top level domains than sub-domains..
#5. You Can Earn More Money: When you are on custom domain, you have greater chances of guest post offers, sales banner, Product Reviews.
Direct Advertisers will advertise at platforms where they find quality traffic as Subdomain holders are often underestimated even if they have a more Traffic.