It's not a destination for tourists. I've heard there's a saying that goes something like the people of Lake Titicaca dance all day and Juliaca is where work gets done. I wouldn't pick to stay here. It was the best airport option after flying from Cusco and wanting to see Lake Titicaca.
Agree with Thais: Juliaca is the only place in Peru where I felt unsafe. Many collectivos to the charming small towns on the north side of Lake Titicaca leave from the market here, but the buses into town often drop you off on the side of a road far away from the market. If you must connect here, do so only during the day - and be prepared for chaos.
Juliaca doesn't have much to do, and for a tourist perspective you would only be passing through to use the airport connecting the Peruvian Altiplano with the rest of Peru.
Juliaca is an extremely poor city that serves as a landing base for counterfeit from China, since it has an international airport. You'll notice that all houses are unfinished, that's because that once they are finished, people have to start paying taxes, so they just leave it like that. Streets are not paved, traffic is insane and nothing seems like in place. You'll drive by on your way to or from Puno, but I wouldn't advise getting off the bus here, ever.