I thought that if you set the engine cold it doesn't matter as long as you have hydro lifters, becasue they take up all the preload you give them. ???
Not true. There's only a limited amount of travel. That's why the instructions always say "take up the slack, then add a half turn." Valve adjustment ALWAYS matters. One of the primary reasons for hydraulic lifters is lack of noise. The hydraulic design keeps all of the parts in contact with each other all the time, so there's no clicking as with solid lifters. Also, the adjustment process is a little more forgiving.

You can lash the valves either hot or cold, but the preferred method is hot. Loosen each one until it clicks, tighten it until the click goes away, then add a half turn. (Some folks use 1/4 turn, 3/4 or a full turn.)