Is it totally necessary to have https for a small blog??
No its not necessary. Unless you have money transaction page.
It may increase your organic traffic for a little while but I assure you it will not stay much long. So, why do it. if its not needed in your site.
As just like Frank said earlier its unnecessary if you don't have a money page.
Not all websites need to have HTTPS encryption because sites like banking, government, etc are recommended to have this.
It's not necessary. But having https will help your site better in SEO and end users point.
Thanks for the information guys.