TL:DR a popular abbreviation for saying: "too long didn't read" commonly used after forum posts that cover a topic with extensive explanations thus resulting in long posts that some people apparantly find too long to read.
Essentially what people are saying when they say TL:DR is that whilst they want to voice their opinion they have absolutely no interest in listening to your opinion first.
Commonly used by trolls to derail forum threads / instigate arguments or by people with very very limited attention spans that never were going to listen to your opinion even if it had been compressed into 2 sentences.
People that cater to the TL:DR crowd often don't understand that by trying to compress their arguments in a sentence or two only manage to aggrivate the problem by essentially saying it's ok to say TL:DR (and as a result saying it's ok to be a troll).
By providing a TL:DR summary you either devaluate your initial argument or your argument wasn't properly set up and didn't need as much text in the first place.
In short, you managed to stab yourself in your own back before you even hit the 'submit' button.
Essentially adding a TL:DR summary to a long post is saying: Hey you don't have to read the post, it's not that important, just read this summary and you'll know everything I wanted to say without all the fluffy words.
Not only that but you literally invite people to post comments that reply solely to your TL:DR summary thus throwing your carefully crafted opinion completely overboard.
In which case you might as well only have posted the TL:DR summary and the value of your 'full' post is deflated accordingly.
Understand that while your posting length will indeed affect how many people read it, it also affects what people read it. Good posts, no matter the length will draw in an intelligent and colorfull crowd even if they span multiple pages.
So fellow bloggers that frequent this here blog, I ask you, to your own benefit, please do not cater to the TL:DR crowd for it will not increase the value of your opinion or blog.
Value your own opinion, think it out, write it down and if it's long? People will still read it because your posts are good even if the trolls TL:DR.