If you purchased Lightroom 5 then you will get all of the updates for that version. But when Lightroom 6 is released you will be required to purchase the upgrade If you want to continue to receive the updates. Then all of the updates for Lightroom 6 will be free. If you go to the Creative Cloud method, you will always receive the latest updates regardless of what version is current. But if you ever decide to end your subscription the develop module will no longer work. But if you have an older version of Lightroom you can go back to using it. It's your choice. Apparently a lot of people really like the Creative Cloud option. Another benefit of the creative cloud is that you have access for Lightroom Mobile automatically. With the standalone version you will have to purchase some sort of subscription in order to use Lightroom Mobile.
What Jim said but to put it in a nutshell, you'll get updates to the version you purchased, you'll cease to get any new versions or the functionality they provide. So if you buy a perpetual license for LR5, you'll get dot releases like bug fixes and new camera support but no new features.
There's no right answer here, you can however do some math and see what the cost of upgrades will run you over X number of years versus an ongoing subscription. If you are the kind of user who doesn't always update to each new version (LR 4 to 5, LR 5 to 6), the perpetual license may be better for you. But if you're like many of us, who upgrade to major new versions every time they come out, subscription might be a better route.
The equation is more than Lightroom (Cloud) versus Lightroom (perpetual).
Bear in mind that with the $9.99/month subscription you get
- Photoshop CC 2014 (+ all major upgrades and minor updates)
- Lightroom 5.5 (+ all major upgrades and minor updates)
- Lightroom Mobile
- Bridge (not that you're likely to use Bridge as well)
- some extras such as Cloud storage
The downside is that when you cancel your subscription, or let it expire, then you can no longer use the software.