Just sharing my personal experience here:
I agree. You can even encrypt the email so you can trace back a particular license to a user in case it is distributed without your permission and cut this user from further updates. Updates are quite useful to motivate people to buy your plugin once it has been cracked so the last thing that you want is to give them to the users who are using another license without permission.
Attaching the license to a machine is a nightmare because users change machines quite often, every OS has little variations about the id’s, etc. Maybe companies like PACE can deal with all the details of it but for a small dev, I felt this was too much work knowing that you will be cracked anyway and there is a big risk that this annoys your honest users.
I know some users that aren’t always connected to the internet (me 
) and I’ve read some posts of people who used cracked versions of the plugins just because they couldn’t use the copy they bought in offline machines. Considering that OS are nowadays non-optional and can add bugs, I think that it actually makes a lot of sense to have your recording studio computer offline.
I’m happy it worked for you. I accidentally made a mistake and removed the protection in my plugins. In my personal case, 1 month later the internet was seeded with uploads of the free installer! 
It sure gave them some exposure but well, the sales dropped quite dramatically (more than the 40% that has been mentioned several times in the forum).