It can get very uncomfortable when you have to sit for a prolonged amount of time on the ground. Every Tisha B'Av, I go through the whole ordeal of having my legs fall asleep, etc.
This year, I was away from home on Tisha B'Av for the first time in many years. The shul where I went to this year was a very small place, with very little wall space. All that space was taken right away, and I couldn't even find a spot where I could at least lean back against.
But someone did me a huge favor: he shared his couch pillow with me, and we sat back to back, leaning on each other for support!