Google Voice Lite is a modified version of Google Voice for people who do not want a Google Voice number, but want the other features.
So with Google Voice Lite, you will still get voicemail sent to you like email; voicemail transcription into text that can be forwarded to you through email or SMS; custom greetings for voicemail; and international calling at VoIP rates, and free to any phone in the US and Canada. Features like call recording, screening and call forwarding will not be obtained. For instance, you will not be able to use Google Voice to ring multiple phones through one single number.
Why GV Lite? The full GV service is free, but some people choose GV Lite because they don’t want to change their phone number. So, they just register that number and use the offered features only as these fit their requirements. They have the option of porting their number (using their existing number as their Google Voice number), but this requires a fee, so many prefer not paying and opting for Lite.