Disclaimer: The below statements should involve the word "usually", as there are exceptions to most of them, depending on hardware, filesystem, software, and OS at play.
Some key points that can serve as guidelines:
- Writing data to disk takes longer than reading. (although the difference is very small)
- disk I/O doesn't really take much processing power in itself.
- disks can read/write faster than the network can transfer.
Ergo, the amount of work on both ends is roughly the same, but the receiving end needs a bit longer to write the data to the disk. However, the speed is likely to be bottlenecked by the network speed
What you want to keep in mind is that the server can have multiple clients connected to it and therefore might need properly scaled hardware to be able to serve them all without transfer speeds suffering. On a proper modern network, this basically means that you want to ensure that the disk is able to keep up with the network. Say, if a few clients end up saturating the network bandwidth, the fileserver needs to be able to have disks that can keep up with the transfer rate.