Ultimately, you have to do what is best for your DD. I did opt out my oldest DS one or two years during the middle school years but everyone was more than okay (he's sick/disabled and educated through their Home & Hospital division and never physically set foot in his enrolled school). I think in general some schools are actually glad to see students with disabilities opt out.
I would never opt out my two younger kids because our state tests are used for placement as well as provide substantial information not available from other tests. Our district also uses MAP, which may be useful to benchmark general progress in knowledge but would be a poor determinant, for instance, of ability to handle our specific GT Language Arts courses. This has to do with our district's heavy emphasis on literary anaylsis and writing from grade 1, which mirrors the state testing. There is also the comprehensiveness issue. For example, DS completes the MAP reading testing in about 30 minutes but needs a couple of hours to complete the state reading/language arts testing. There is a huge difference between reading a short blurb before clicking on a multiple choice answer and preparing a multi-paragraph essay after analyzing/pulling information from a couple of long documents.
I also think that you have to look at the culture in your state and district. DS/DD's school don't prep or otherwise make a big deal about the state testing but parents are told when it is and to make sure that their kids are well-fed and well-rested on test days and the school kind of celebrates when everyone is done. This means that in particular, if you have social kids, they may feel out of sync if all their friends talk about their experiences and they have no clue.
