Is there any reason not to sell money pins?

Unlike the original TWEWY, there are no trades in NEO: TWEWY that require money pins. With that said, ShibuPay Autoload cannot be disabled once unlocked, resulting in a few reasons you might want to avoid unlocking it.

• Later in the game, you can unlock social links with ShibuPay Bonus, which allows you to earn 5% more money when selling pins. These can be unlocked during Week 3 Day 2 and Week 3 Day 4.
• According to Chronocidal, ShibuPay Autoload will continue even if your wallet is full, leading to wasted money. (I haven't been able to test this myself).
• The autosell can make it difficult if you want to keep one copy of each pin in your inventory. However, it doesn't affect yen pins collected before unlocking the ability.

Aside from the first point about waiting until ShibuPay Bonus is unlocked, I haven't found any reason to avoid selling money pins.