For me, MBTI does play a significant role in a relationship. I've found that I get along much better, and communicate much better, with other Intuitives. I've been in relationships with both Intuitives and Sensors ... and I can only go so far with a Sensor. It usually remains pretty superficial. I find that I can craft a much deeper relationship with another Intuitive.
This does not mean however, that I should be comfortable in a rut and attribute it all to this being the way I am according to MBTI. I do believe in exploring and growing other aspects of myself that might not be my preferred functions. I also believe that a relationship depends on more than MBTI ... it is simply one of my cornerstones for understanding and growing a relationship. If I know the needs, desires, and preferred communication methods of my partner ... then I can be more responsive to them.
I didn't know anything about MBTI when I got married. But, for me, a clueless INTP, MBTI has been a great tool for understanding people, something that comes much more easily for INFJ's. Sure, it has limitations, but these are nothing compared to my limitations in understanding people, at least at the time I learned about MBTI, about 25 years ago.