As noted, it's probably best to look at multiple crowd calendars to try to get a sense of what the park crowds are going to be like. Two other commonly mentioned crowd calendars here on the Disboard are
IsItPacked and
RMH Travel. If all three are indicating it'll be crowded, it'll probably be crowded. If they're split, it probably means it's hard to know and could go either way (although, lately, it seems like
Disneyland is always crowded).
In terms of Touring Plans specifically, like most crowd calendars, they aren't going to be 100% accurate. They did recently try to re-do they statistics to do a better job of estimating crowds, but they did have a tendency to under-predict crowds in DL and over-predict crowds in DCA. I do like that they present
"after-the-fact" comparison so you can get a sense of how well they are doing. Basically, I would look at TP's crowd numbers and use a margin of +/- 2.0 to get the range of crowds you might experience. I think the biggest issues with Touring Plans are: 1) they only use attraction wait times to predict crowds, so it doesn't necessarily work well for large event days when there might be a lot of folks in the parks, but not necessarily riding attractions (e.g., marathon weekends), 2) they use past crowds to predict the future, so if there are unexpected events or things that are different from the past, their statistics don't always capture that well (e.g., when new events debut in the parks), and 3) they crowd numbers skew towards the higher end of the spectrum rather than being distributed (i.e, there are more days above 5 than below 5).
While on the older side, this post still has a pretty good explanation of the skew issue with TP:
http://www.disboards.com/threads/wh...ing-plans-website-dlr-crowd-calendar.3196851/