with rdf the following things happen for me and my guild:
1.) it allows us to help our limited time guildies get on, run a dungeon, and log off in short order so they dont anger their wife. this is a good thing.
2.) it allows my guild to put together lowere level runs with just 3 or for members, que in to get empty slots pugged and be running within minutes. this is a good thing that LFG tool has failed to provide.
3.) it allows me as a player, when my guild isnt running anything in particular, to grab my tank or healer or dps im working on and que up to get a run in, usually after that character has gone to collect up the dungeon quest in the world that arent in the dungeon already. this is a good thing.
4.) when i have some down time and still want to play, i can hop on, grab my tank and que in solo to help other faction members outside of my guild get runs. another thing that the Current LFG tool has failed me with. so with rdf, this is a good thing.
5.) rdf has the ability to votekick so im not subject to one persons will and no one is subject to jsut mine and those powers are limited in use so a group cant just que up to kick people out.
6.) rdf generally provides players with a better starting attitude since they didnt just spend an hour of their time sitting in town waiting on a group. it generally leads to more talk at the end of the run, and even has ended in guild and friend invites being sent. something LFG tool has failed me on but RDF gave me in spades back in the day. this is a good thing.
7.) i can que into rdf to run dungeons like ragefire chasm, deep in the heart of ogrimmar, while hunting the dungeon achievements without having to spend 3 hours running, rezing, corpse run, respawn, running, rezzing, corpse spawn, respawning trying to reach it.
8.) rdf allows me to quest/farm/fish/craft/work the AH while waiting on que pop without having to monitor the tool or a chat channel, then teleports me to run. when finished puts me right back where i started. this is a good thing.
if you would like me to continue i have several more good reasons that LFG does nothing to provide for. but im hoping you get the gist.