Buy/sell option allows you to buy/sell tokens that are in circulation from other traders. Subscription/redemption gives you and option to force binance to create/burn new tokens for you and back them up with real bitcoins on the market. This option is more expensive (additional fee) and is used mostly in extreme cases when there is a difference between BTCUP/BTCDOWN spot price and value they represent.


"Leveraged tokens are traded on the Binance spot market. In addition, they can also be redeemed for the value they represent. In this case, you’ll need to pay a redemption fee. In most cases, though, you’ll be better off exiting your position in the spot market rather than through the redemption process. Exiting through redemption will typically be more expensive than exiting on the spot market unless something like a black swan event occurs. This is why it’s almost always recommended to exit your BLVT position on the spot market.
You’ll see a term on the leveraged token’s page called Net Asset Value (NAV). This refers to the value of your leveraged tokens denominated in USDT. When you redeem your tokens, the USDT you’ll get will be determined by the NAV."
https://academy.binance.com/en/articles/a-beginners-guide-to-binance-leveraged-tokens-blvt