How does double desynth work?

[Renius]

Is it better to lvl two professions and lvl their desynth? Does it somehow combine the two? I understand that like in my case a goldsmith and LTW will desynth totally different items and diff material but what is the correlation between the two, or is there one?

[Dustytome]

It's separate for each craft, you just have enough points in the end to max out three of them.