You may want to secure it. I had a vertical run of 3" conduits each with 3 innerducts to a roof penthouse. The electricians tied mule tape around the 3 innerducts where they came out of the conduit to "secure" them in place. But in pulling fiber through, that group of 3 ducts fell down into the 3" pipe. So I pulled it back enough that I had at least a foot of innerduct above the 3" pipe and secured each one to the wall with a conduit clamp (I think one hole straps fit it tightly).
If you need to pull hard on the fibers, the innerduct may move with it so it is best to secure it.