Sometimes it is important to register a domain name with hyphen so that your competitor does not register it to their advantage. Hyphen is generally considered not good in domain registration but it does not mean that you should not consider it at all.
For example if you are registering myexample.com it makes sense to register also my-example.com along with my-examples.com myexamples.com. By doing this you virtually close all entries to other domain registrars or companies to use a different set of version for your own site name.
Dot com is a king and it will remain. It also donates that a company is international and can supply its services and solutions to the people around the world.
Some companies along with dot com also opt for .net or .org along with cctld of countries in which they have operation.
Although registering so many domains with all alternatives is an added advantage but it is generally not so important for every company as the budget and their financial positions differs.
One thing companies can do to protect their online identities is through the registration of trademarks for their distinct domain names.
The above are some points which are essential for domain registration.