Having IP address for a domain, does it help regarding site speed, search engine gives it a plus, any info for or against having unique vs shared IP?
Can't get what you're talking about. Be clear. Talking about IP address, search engines can't read domains through URL. They identify it through the IP address. For that you need to have a unique IP for your domain.
I mean, for most sites that exist, they are on shared server where one IP is assigned to numerous sites (domains). Question is, does it help in SERPs if you have a single IP for one domain?
I cannot see any pros to include site's IP address in SERP, and that way Google encourage the depletion of IPv4
Sharing an IP address or having a unique IP will have no impact on your search ranking. Google doesn't think of sites by their IP addresses, just their URLs. Large sites use dozens of IP addresses and one IP can serve multiple high ranking sites. SSL Certificates certify a domain name, so sharing an address won't hold you back.
yes, some times it does matter what is your IP. while you are on shared ip address, and any other site operated by some other person is violating rules or having bad offense content search engine generally bans such IP. And as you are on shared network your site also will not be crawled by search engine. But it will be rare case, however you will not know it until you search for this in deep, why your site is not crawled. Another thing is there are also class range for each ip, you may check your ip address having which class by this link there is online tool available for ip checker having dedicated IP will not be a requirement until unless you are a big company like google and do not want to share IP !
No. The unique IP Address will help the delivery of emails to the target. If there is an IP Address that is used by 300 websites, there is a greate chance that people from your IP address to try to spam, making the email accounts to block it.
There is nothing like Search Engines or ISP give preference to any specific IP-address. Whatever IP you choose everything will remain same.