LFR isn't healing and won't make you a better healer. Do 5 mans / challenge modes if you want practice. then go to raids.
LFR makes you forget how to heal.
If you go into LFR with the *wrong* attitude, you won't be practicing healing.
If you go in there and use the "raid-ish environment" to help develop muscle memory for your cooldowns, it can be helpful You just have to... uh... suspend your disbelief that any of it is important ;)
For example - for a Disc priest, you could:
-focus on remembering to make good use of PW:B, Pain Supression, and Mindbender (... or good Shadowfiend use and KEEP SOLACE ON COOLDOWN AT ALL TIMES)
-work on Rapture timing better than is often possible in 5mans...
-improve your target selection for PoH efficiency...
-work on ensuring that Evangelism *never* falls off you (until you pop Archangel of course)... of course, for that to be of any relevence, it presumes you're trying to make use of abilities other than Atonement healing.
As Venomheart is suggesting, no, none of it has much importance for whether the LFR succeeds or not. However, LFR *can* provide an environment some people can use to do a bit of practicing of things which aren't very practice-able outside of a raid environment.
I'd also suggest BGs or arenas. My Disc priesting took off, back in Cata, when I started doing even just casual BGs and arenas with a friend. PvP is an unscripted environment; every fight is different because the match-ups are different every time. If you're willing to dust yourself off, get yourself back on your feet, and let go of your wounded pride every time you die, it can be an amazing training ground for all sorts of instincts which are transferrable back into PvE healing.