I think Valve uses tf/mapsrc, which lets you use one obscure in-game console command to place physics props in your .vmf files
Pretty sure that command works just as well if you setup hammer's default folder to point at whatever .vmf you're using it for though...
Personally I have a mods/tf2/mapsrc folder on a separate hard drive with all my modpacks & sprays
Inside that I've got folders for each map, and 2 folders for sketches (detail & objectives)
Also I have a few other general folders, once for contests, one for decompiled official maps (reference)
Hammer is also setup to save it's autosaves in this folder for me, instead of the default C:/HammerAutosaves
The folders dated Jan21st are from when I moved the folder to my new PC