I remembered about these while creating one my missions, I wonder why they didn't make it into the final game, seeing as how they put vertical ones in.
 
Go to the 50 sec mark if you need a reminder...
 
  

I can't really see much use for them. The vertical lines are for quickly scaling buildings, but never have I felt a need to quickly get across the side of a building.

As said above me, they don't really have much use.

Because I don't want to be climbing up the side of a building when I climb onto one of those and go flying to the side. 
More annoying than useful it would seem 
Eh, what do I know 

I think that was the reason. Also, such lines would also make the rooftop grind lines less used.

Because I don't want to be climbing up the side of a building when I climb onto one of those and go flying to the side. More annoying than useful it would seem Eh, what do I know 

I've seen them in a gameplay video of a guy who got his copy early, at 31:40: http://www.youtube.com/watch?v=3B2CQGWdyuE

@ViciousReiven said:

I've seen them in a gameplay video of a guy who got his copy early, at 31:40: http://www.youtube.com/watch?v=3B2CQGWdyuE

Those are not the ones we are talking about.

@Pie said:

Because I don't want to be climbing up the side of a building when I climb onto one of those and go flying to the side. More annoying than useful it would seem Eh, what do I know 

I think this is the reason. They found when people were climbing up buildings they were accidentally grabbing onto them and zipping off to the side.

@ViciousReiven said:

I've seen them in a gameplay video of a guy who got his copy early, at 31:40: http://www.youtube.com/watch?v=3B2CQGWdyuE

Those are not the ones we are talking about.

@ViciousReiven said:

@Cloudenvy said:

@ViciousReiven said:

I've seen them in a gameplay video of a guy who got his copy early, at 31:40: http://www.youtube.com/watch?v=3B2CQGWdyuE

Those are not the ones we are talking about.

Blah I read the title as verticle for some reason.

Haha, no problem!

Oh yeah, I forgot about those! I think they were in the demo I played at PAX last year. They problem took them out for the reasons above.