I can't add much to what Squatchy says - only my experiences...
I'm probably a bit over-sensitive when it comes to any perishable adjuncts I put in my meads (fruit being an obvious one). I won't leave it in my must longer than maybe 17 days, and prefer 14 days.
I DO think having a lot of fine lees in suspension can effect taste. I try to get my meads off the vast majority of lees, age, tweak, fine, then filter. Now, I haven't tested a few different ways to do this, but I really try to fine only once. Doing it twice doesn't hurt anything as far as I've noticed. So, I get my meads to clear (mostly) by cold crashing, racking off, and then aging. Depending on what I'm doing, and what I think the mead may need, I may fine twice. You can get a good idea where a mead is going at about 6 months, but if you fine at say one month, then back-sweeten with honey, you're mead will need to be fined again.
In my experience, nearly anything you put/leave in the mead can/will impact flavor if not handled right. The exception should be fining agents - they should not impact the flavor. Others may have tested pectin (when you end up with pectin haze) in some bench trials, but my only experience with pectin haze was that it did not seem to impact flavor. It's a pain to get rid of, but doable.
SG readings are necessary, and can tell us a lot, but final SG of any mead is not really what's important. What's important is how it tastes.