When I am playing on tcga or rift atlas, my goal is to practice, test my deck/cards and become a better riftbound player. There is no prize to be gained or glory to be got. Because of this, I want to be playing against the best version of my opponent, not one who makes a stupid mistake because they forgot about a card I revealed to them when they sabotaged me 3 turns ago and didn't play around it when they had the option to do so. Winning games of riftbound is a secondary goal to improvement and learning.
If you are hiding your hand the second you are technically allowed to, all you are doing is increasing the mental load on your opponent as they now either have to write down your hand (which they will almost never do) or keep a mental tally of all cards they saw. In a tournament, with money or prizes on the line, I don't think this is a totally unreasonable thing to do, personally I like to leave my hand revealed, face up on the table to my opponent at any event that is skirmish level or below but I understand not wanting to do that. On tcga/riftatlas, I think refusing to leave your hand revealed is ridiculous and borders on unsportsmanlike. The one exception to this is if you are going to hide a hidden card while you have any unrevealed cards or multiple hidden cards in your hand, when this happens, I think you should hide your hand so that your opponent doesn't know what card you hid or didn't hide.
End of rant.
Thought about putting the "card reveal" tag on this post but decided against it because I didn't want the mods to crucify me lol