In case of small /home partition there is Steam Library feature, but it's still not fully implemented on Linux: https://github.com/ValveSoftware/steam-for-linux/issues/111 (we can create Steam Libraries but we can't choice it while game installation).
By default steam install dir located in ~/
It would be nice if the first run of Steam would have dialog box that allows you to choose Steam install dir.
This is necessary in the case of small size of /home partition.
Possible solution - dialog box create symbolic link ~/Steam -> /path/to/your/dir