Blocking on Twitter is mostly pointless -- it shields you from seeing the troll's tweets, but everyone else can still see them. And you still see their tweets when they @-mention you, which they will. Blocking on Twitter might as well not even exist as a feature. It does very close to nothing.
By contrast, if you post a picture of your dog on Google+ and a troll says something horrible about your dog in the comments, you can delete the comment and block the troll. Boom! Done! You will never see that troll again on Google+, and they will be banished forever from commenting on your posts or participating in the conversations you start.
After you block them, the troll will see nothing on your profile as long as they're logged in. If they log out, they can see your public posts -- Google+ posts are, after all, public pages on the open Internet. But they can't comment (i.e., troll you) without being logged in.
The troll can, of course, create a new account with a new fake name and come back to troll you. But because it takes some time and effort to create a new account, and they can be blocked with such little effort on your part, trolls almost never do this on Google+ for any length of time.
Blocking on Google+ is the opposite of blocking on Twitter. On Google+, the troll is gone forever. On Twitter, the troll continues to troll you without restraint. The only effect is that you have your head in the sand while the troll reaches all your followers.
One other point of differentiation: On Twitter, you can't direct-message (privately message) someone unless they follow you. So to reach out to someone new you have to message them publically, which alerts trolls and enables them to troll the person you're contacting as well -- they get to you by going after everyone you interact with. On Google+, on the other hand, you can privately message strangers without the trolls knowing.
How to block trolls on Google+
When you encounter a troll, click on their name. That will take you to their profile. In the upper left corner of their profile page, you'll see a box with their name, information about who's following whom, and in the bottom row a bunch of cryptic icons. The icon on the right is a down-arrow. Click that and choose "Report / block," followed by the troll's name. Click on the "Block" check box at the top. Optionally, you can choose some options for reporting the user to Google. Click "Done."
You can also do it from the comment itself. Click the "Delete comment" icon (a circle with an X in it), and you'll be given the option to block the commenter as well.
Sign up for CIO Asia eNewsletters.