It was a definitely a "let's add sex appeal" moment. I quite like her as an actual character though (besides the weird Chakotay thing), they're lucky Jeri Ryan is a good actress. The ratings went up pretty much immediately after her introduction so I guess we played right into their hands haha.
The Chakotay and Seven relationship isn't canon in my opinion. Seven and the EMH? Adorable! Seven and Harry Kim? Sure! Seven and no one? Even better! Just another reason to hate Berman.