In the parts of the forum that shall not be named, there was a disagreement about the design principles for official cards. One person thought there was a soft rule that cards that can trash or Exile other cards don't have 'you may' on them without a good reason. Cards like Spice Merchant have 'you may' for tracking reasons, cards like Sanctuary have it because they provide a benefit other than the Exile; Mercenary has it because it can activate Urchins; Death Cart has it to prevent getting the +5$ twice with Throne Room. But, according to this person, all the cards that usually wouldn't do anything without trashing/Exiling and don't have tracking issues, like Forager or Bounty Hunter or Remodel, are mandatory. Is this a real rule you've followed?
I don't have any rule like that, specific to trashers, no. My "you may" rules are:
- I don't like having a mostly pointless "you may"; if you would mostly achieve not doing whatever it is by not playing the card, or if you will almost always choose the option, then it probably doesn't say "you may." "You may" wants to be used for things where it's really an option, you will play the card and sometimes go one way sometimes the other.
- I use "you may" as a keep-you-honest thing, like on Moneylender; "Trash a Copper from your hand" means you might not trash one and be cheating, and "Trash a Copper from your hand (or reveal a hand without one)" is longer than "You may trash a Copper from your hand."
- In some cases there's a "do x to have y happen" where it reads much better with "you may."
- Reactions of course naturally say "you may."
- When it could go either way, it comes down to power level or fun.
- As always, on pre-Adventures cards, sometimes there wasn't a good reason. Farmland omits "you may" because I required the text to fit in a certain amount of space at a certain font size, and "you may" didn't fit.