From LightWiki

You've set up your major scene, you have just two days to get it rendered, so you don't want to waste time with compiling an animation at the end, so you render to an animation. Wrong move boyo.

The render progresses nicely, but then about two thirds of the way through the 1370-frame render, you have a tiny power cut. The power only goes off for 30 seconds, but it's enough to kill your computer. You can't "carry on" with your render, you have to render it all again from scratch - roughly 920 frames down the pan. If, on the other hand you'd rendered to images, you could just render the remaining 450 frames with no trouble. Unfortunately, while a power cut might be unlikely these days, there are numerous other things that can cause problems with renders that you just can't get back from, so rendering to still frames is still a good idea.

Other reasons it's a good idea, as if this weren't enough:

• Animations are going to be compressed. While you may get away with resizing that DiVX animation you've made, it's unlikely. However, you're far more likely to get away with resizing the 1370 still frames you have on your hard drive...
• If you are using a render farm, or even if you are just using separate machine to render the frames for your scene, you don't have any choice, you have to render to frames anyway
• There's no animation format that deals with HDR imagery in a nice way, at the moment, so rendering to frames is the only way to create something that can be tweaked afterwards
• An image sequence is far easier to deal with in LightWave than an animation, since LightWave only needs to buffer a few images either side of the one you are on
• Rendering to frames is framerate-independant, meaning that you render the amount you need for your animation and you can do the retiming in post. It's also easier to clip every third frame by simply deleting to speed things up, or duplicating every other frame to slow your animation down
• If you render to one specific sort of animation and your client decides that they want a different format, then you will almost certainly have to re-render

For the simplest way to compile those stills into an animation safely just using LightWave have a look here.