for me the idea is as follows. they give you the chance to add some texture and visual interest in a solid color tie. solid ties are certainly the most versatile ties, but they can also be the most boring ties. the grenadine weave negates a lot of the boring. you can get a similar effect with a slubby silk shantung or linen or wool or cashmere, but they tend to be more seasonal and sometimes maybe not formal enough, depending on the wearer and occasion. the grenadine is kind of like the perfect mix for creating a super versatile and not boring tie.
I agree to all of this. But I still say it can be had that most combos people post here can also work with some other tie that's not grenadine or solid. Why solve a solid boring tie by going grenadine when you can solve it by adding an actual patterned tie? Not saying it should never be solved this way, just saying it could be solved that way less often than it seems like it is.
It's like I'm hearing my favorite song on the radio over and over. Great for the first few times.