With the upcoming release of Flex raiding - the fourth raid difficulty option - the question has once again arisen as to why 10 man LFR hasn't been implemented in-game as of yet. Despite the fact that 10 man raiding provides an environment that is less taxing upon your hardware there really isn't any clear advantage to providing it as an option. Hopefully I can clear the 10 man LFR issue up for the last time. Here is why I don't think 10 man LFR should be made available:
Raid composition has a greater importance in 10 man. Certain buffs are necessary (arguably not since LFR is so easy) and since LFR places you with completely random classes, this composition requirement will not always be met.
The biggest reason that this feature hasn't been implemented is that in 10 man more players will be required to pay attention. 3 DPS going afk or autoattacking the boss in 25 man has far less of an impact on the raid compared to the same situation in 10 man. On top of this those AFK players won't be able to blend in as easily (not advocating that as a good thing but it's true).
Here is a relevant quote taken from the official forums by Takralus:
"Having the LFR group size set to 25 allows for a more forgiving experience should errors be made by individual players - after all, we believe raid finder groups should be a fun way to experience raid content without feeling too punishing to new or inexperienced raiders."
Here is a link to the above post: http://eu.battle.net/wow/en/forum/topic/3061921536#2
With only 10 players necessary for an LFR run to occur surely it would mean mean shorter queue times? This is not the case. As a dps I wait an average of 20-30 minutes to get into a 25 man LFR run as of now - this all depends on the time of day of course. 17 dps are required in a 25 man environment whereas only 5 or 6 would be necessary in 10 man. The ratios work out to the point where DPS queues would sky rocket causing much frustration for many players - especially those who use LFR as their main source of raiding. Instead of waiting 20-30 minutes it would be closer to an hour (guesstimating).
Hopefully this thread rounds up, once and for all, the question of whether 10 man LFR should be an option or not.