Advantages: tiny amount of rack space and current required for a combined VCA and VCF, gives the classic Buchla sound (though that isn't based on a hands-on comparison). The ability to use a clock to trigger a variable release envelope also potentially saves on an envelope generator.
Disadvantages: Thin panel and small knobs are a little fiddly to use. Although it doesn't deviate from the unit's stated purpose, the LPG sound is a lot more limited than a classic VCF and VCAin terms of variation.