I often put BYOH on my cleric's LFM's. My intention is to hopefully get people who can heal themselves to at least some degree, rather than getting the players who don't carry pots or wands because they think a healer should do ALL the healing.
However, I still heal people all the time. Why wouldn't I? If they are having trouble and I can keep them up, it is in my best interests to do so.
If my LFM reads "BYOH" and someone joins and starts yelling at me when they drop from 250 to 230 HP, I tell them it's BYOH and they should drink a pot. If they calmly and politely ask for a heal when they are dropping below 50% or 25% health, I will always heal them.