That doesn't make sense.

If you are low on mana, that means you were succoring tons (or spamming adloq...which i dunno why you would ever do).

If you were spamming succor you should've placed a SS, if spamming adloq you should've used lustrate.

Which is basically...if you are low on mana you should have 0 stacks.

If you are low on mana and you have unused stacks, that was your own fault that you wasted those potential XD

So yes, while I agree that if you are low on mana, and somehow have excess stacks, you should use them, it is a horrible practice and means you weren't doing things efficiently.

Also I guess if lustrate isn't doing more than your physick on a tank, something is very very wrong, or your tank is extremely undergeared compared to you.