there are 2 ways to test the result before burning, so you do not need RW in most cases. Of course this is for playing on computer.
1) If the result is ISO, mount it in Daemon Tools and play from this virtual drive.
2) If the result is files in VIDEO_TS folder, just use DVD player on that.
It is easy to test with freeware Windows Media Player Classic program, it can do both of the above. (the mounted ISO DVD is actually in File/Open CD-ROM)