And if you happen to reach floor 350+ and get items with crystalline, they can boost chances to find skyblue items (crystal legends) by a certain %. Another good boost is the treasured ascension perk which gives an easy 200% crystal legend find and eternal legend find. The eternalized /crystalline combined with ascension is really good for farming eternals/crystal legends wigh specific crystal affixes for getting those crystal affixes without having to use obsidian.
In the late game, when you have enough gold, you can convert quite a good amount of eternals that feel completely useless to you for a higher chance fo get ultra rare crystals (jasper-obsidian). These ultra rare crystals are extremely useful in crafting. Also you can convert certain crystal legends with crystal affixes you don't plan to use (unless you need it for a build) and even then, just keep as many crystal legends as possible and don't convert them (it is up to you though).
There are chances of eternal items with crystal affixes too which can be somewhat useful depending on your build as well as a chance for eternal rare legends if need be. I am not sure if its possible but there could be a miniscule chance to get crystal rare legends with affixes that can be in crystal form. Eg, total hp on nadroji amulet could be a cryatal affix on nadroji amulet but i can't confirm if this is true or not. I have found eternal rare legend items (nadroji ring amd robe 2.0 versions) but never a crystal rare legend so i am guessing there is no such thing as a crystal rare legend,
This is all up to you though and every player decides how they truly want to play.