I don't use sealer in normal pruning,....only on some large limbs I take off or ugly damaged wounds from animals or other injuries I use the Dr. Farwell grafting seal.

This really helps the cut from drying and cracking, where
water and other bad stuff can penetrate...eventually a place where it can rot.

Some do, some don't. I never have, having been told that it inhibits the tree's natural ability to heal. Konrad knows and does a lot more than I do, but even so I think you'll find it a matter of controversy.

Its called prune and seal I use paste better than spray can. Seal out moisture water rot wood. Its more good practice than need I use on new planting of tree's because first year transplant growth slow healing time longer.

As Mark pointed out, there are varied opinions about this. Some insist that tree sealers seal in moisture causing the wood to rot faster. For myself, I don't use sealer.

There have been numerous studies that show sealers offer no benefit to wound healing, but I'm not aware of any that show sealers beneficial.

I'm not saying they are not out there, just that I've not seen them. If anyone has any research showing sealers are helpful, I'd love to read it.

A few years ago there was an arborist over on one of the GardenWeb landscaping forums who posted he painted a concentrated solution of copper on large wounds. He claimed it protected the wood from rotting while the wound healed. This made sense to me, as copper is a natural bactericide/fungicide and one of the components used in treated lumber.

Thank you very much for all of your responses. I have to think about what I want to do.