If you have not read an issue of the magazine to which you are submitting, do not submit. If you read an issue and do not like it, or (which amounts to the same thing) do not grok it, save everybody's time and do not submit. There are many towns in poetryland, and you can "take a train" to "a different town" very easily. In this "different town" you may enjoy "the buildings" better, and your work is much more likely to be accepted by the "town planning comission."About grok: I think if I didn't send until I was sure I had "grokked" the magazine (which sounds like more of a complete intuitional grasp than simply "liking"), I'd probably be waiting 'till kingdom come.
Sometimes I send to a review because because I sense -- even not reading it in its entirety -- that poems I have might fit in. Sometimes one issue can be misleading: I've read issues I've disliked of magazines that I later learned published poets (and even poems) I really appreciate. Some of the older reviews one can get a bead on if one looks through the review AND knows the some of the poets they have published. Then there are occasions where I study a review, think I have something right down their alley that doesn't elicit any interest at all.
I don't send out much, but have a fairly good batting average (over the last 2 years, 1 acceptance of one to three poems for every 5 or 6 five-poem submissions), so I guess I'm doing something right.