Is the "invite based" sign up worth having for a new application or startup?

So, just as the title states, is it worth it? I've seen a lot of newer services try this model, including Google+, Spotify, etc. but I'm not sure if it really created enough value for the services. What do you guys think?

PROs
- Creates a "hype" for your product. Makes people want it more, I guess.
- Gives initial users a more personal feel to the company.

I thought of some more, but you get the idea.

New applications use the "invite based" sign ups model for a number of different reasons. Creating marketing buzz is just one of these reasons. You need to understand why firms do this before you can decide whether or not it is a good idea for your firm. These reasons include:

1. Limited web resources. Letting an unlimited number of people sign up for a web based service, all at relatively the same time, will overwhelm many hosting systems. By controlling sign ups via an invitation system, you control the growth of your system and can match it to available resources. (This is the major reason for Google Plus invitations.)
2. Controlling group membership. You can use the invite system to control who, specifically, gets into your system first. Perhaps you want journalist first, or you want to exclude them. Perhaps you want power testers in first. Whatever the reason, using invites lets you control who joins your system and when they do so.
3. Generating marketing buzz. Limiting membership in a group may make people more anxious to join that group. Their word of mouth helps you advertise, or market, your product or service.

I'm not sure if Google+ and Spotify are the best cases for whether or not the invite system created value--they were both already benefiting from a ton of coverage and widespread awareness before they launched.

Personally, for the website I'm currently working on I plan to implement some form of the "viral invite system ". I see it as being beneficial in two primary ways:

One, it can help me with scaling to match the userbase should I choose to lock new user registration. I'm not expecting an explosion of users to come rushing to try my website/application, but with any growth unforeseen problems will arise and this can help me deal with them.

Two, the hype you mentioned: by giving earlier access to users who share your website out, you can help generate some good word of mouth. There's already a hurdle you have to cross to get users to give up their email address to you, so it's not much of a stretch to encourage an impulse action--getting them to share your link out across Facebook/Twitter.

In addition to Gary's answer, I'd like to add that initial days of invite based sign up acts like a beta stage where you also discover bugs reported by early users and can correct them in time before everyone is on board. This IMO is equally important (if not more) as those 3 points.

The reason I used an invite page was to validate the concept. I put up a couple of paragraphs explaining what the site is about with a subscribe form. This was a couple of months before the site would actually go into to beta to prove whether it was worth building the full site.