I think he meant the peoples own guilds. LFR gives an additional source, and since loot drops are limited, even serious raiding is speed up.
Without LFR you'd have to do additional runs to gear up alts, for them to become valuable alternatives to your core runs, in case someone cannot raid.
There's always a 10 - 20% possibility of people aren't available... 1 - 2 for 10 man... 2 - 4 for 25 man.
LFR helps keeping the flow going even for the more serious raids.