As everyone knows, the longer a word is the better it sounds. Thus, when people add senseless suffix's to words, it only makes the English language cooler. Such is the case when dumb, boring words like "indeed" are changed to long, flowing and luxurious words such as "indeedly." In essence "indeedly" is just the cool people's way of saying "indeed."
In agreement, to agree further more and build upon your sentence. It can also be used to make people think you know what you've talking about, even if you do not.
It's basically the same as indeed, only you get to add an extra word after it, to sound more official and cool. Like bow ties. Bow ties are cool.
"Dubstep is a horribly genere and those who listen to it have rather poor taste."
"Indeedly so, my good friend."