Make a Render Farm Out of Old Computers for a Cost-Effective Way to Speed Up Rendering

Used servers can be bought for very low cost and can make for powerful rendering machines.  These Dell PowerEdge R610 servers are outfitted with dual Xeon Hexacore processors and are around $400 each.


Render Farm Question

Do they just work for outputs, or can you utilize the render farm power while you're working? Say I'm in Premiere or Avid, and I have effects in my timeline, can the render farm facilitate faster renders of those effects?