It should be totally easy. It should be built into Windows. But it's not. There's no straightforward way to transfer files between two computers that would work well in all the common circumstances. But there must be something... Let's see what we can find.
I could use an USB stick. It's fast, easy to setup, highly compatible, and it can handle large amounts of data. Unfortunately I keep forgetting the USB stick. It's never around when I need it.
Windows actually does have a built-in file transfer functionality - the infamous shared folders. Despite several serious attempts, I have never managed to make it work, because of the incredibly stupid way Microsoft decided to secure shared folders. Aside from being incredibly hard to setup, it requires identically named account on both computers with identical passwords, at least in home network environment. That doesn't count as a file transfer in my opinion. It's just file sharing between devices owned by the same person. The feature seems to be designed for internal use in enterprises.
Online storage providers like Dropbox are pretty expensive. The free option is too small to be useful. Also, it's not enough to optimize transfers over local network. I want to actually prevent transfers over the Internet entirely, especially for the huge HD videos. Besides, these services are known to invade privacy.
Skype, Microsoft's favorite chat client, can transfer files. It optimizes transfers over local network. Unfortunately it can only transfer one file at a time. Zipping a collection of large files takes ages and lots of disk space. There are serious privacy issues with Skype too. I should look for a better chat client in any case.
uTorrent claims to utilize local network if possible. It's unwieldy for random file transfers, but it might come handy for replication of content that has been already downloaded by uTorrent. Unfortunately it doesn't work. At least not in my case. The local peer ignores my computer and even when it finally recognizes it, there is next to no traffic going between the two computers even though they are on the same private subnet.
FTP server, for example FileZilla FTP Server, can do the job, but it's almost as unwieldy as uTorrent. Most of my file transfers are one-offs. Any kind of upfront setup is a serious obstacle.
I bet there must be tons of apps that can do this. And I have finally found one: Any Send (not to be confused with identically named cloud service). It will transfer any set of files or folders between computers on the same network. Just Crtl+C the files in folder window, then click AnySend icon in the taskbar and select some computer on local network. The files will be copied into a folder on the selected computer. It couldn't be easier. It has a bonus feature of supporting multiple platforms.
It's probably not the best app around, but it was the first one I have found and it does the job at the moment. It could be a bit more polished in that it could display transfer rate and estimated time of transfer. I am not sure whether it will be able to continue interrupted transfers. It probably wouldn't do that. There are also a few more nitpicks. Nothing serious enough to warrant search for another app.