I'm doing a decoction tomorrow and then another on Sunday.
I do mine in pots so I just add a little heat to keep the mash at the rest temp while I rest/boil the decoction.
I can't really attest to the benfits of a decoction because the only brew I've done it on (in the last 10 years) just
got racked to the secondary. But if the taste of my Vienna Lager at only 15 days in primary is any indication then I can say that they are a good thing. Just the aroma and color of the decoction at the end of the boil seems to indicate that it has a significant effect.
FWIW, I do a combo infusion/decoction like this:
I strike to an acid rest @ 95o F.
Then I infuse to a protien rest @ 122o F.
Then I immediately pull as thick a decoction as I can.
Then I infuse the decoction with a smallish amount of boiling water and add heat to get it up to 158o F as fast as possible and rest for 10-15 min., test for conversion.
Boil decoction 40 minutes (30 min. minimum and not a second less
Add to mash and rest @ 150o F for 1 hour, test for conversion.
Pull thin-mash decoction (pretty much all liquid).
Boil decoction to hot break.
Mash out @ 170o F.
Def more time consuming...but I obv didn't get into homebrewing to save time.