The advantages and disadvantages of the monolithic filters
Advantages:


high order filters in small form factor
adjustable corner frequency
easy to implement


Disadvantages:


limited resolution (12 bit here)
obsolescence can be an issue (probably not on this one, LT doesn't EOL parts often) 
not as flexible as other active filter topologies


How about an example? These types of parts are particularly useful as anti-aliasing filters. Suppose you're designing a data acquisition system, with eight analog 0-5V inputs, and the sample rate is variable from 10Hz to 100kHz. The Sallen-Key topology, for example, lends itself to anti-aliasing, and making it variable over that wide of a range will be very complex, and take a lot of PCB space. The beauty of the monolithic filter is the corner frequency is variable with a clock signal. The part referenced has a 100:1 ratio, so to get a 5Hz-50kHz variable filter, you would feed it a clock varying 500Hz-5MHz. That can be generated from your main microcontroller, and you have a nice single chip filter solution.