The Sweat page currently leads with the 20% off voucher at the top of this page, which takes 20% off your chosen plan when redeemed at checkout and is best for anyone who already has a discount code or prefers to enter a code at payment. This code applies on the website and cannot be used with any other offer, so it suits you if you want a guaranteed 20% reduction on the plan you pick and will be completing the purchase online.
If you already have a code and are ready to subscribe: Use the 20% off voucher above at checkout. It gives 20% off the plan price on the website and is straightforward when you have the code to hand. The terms say it cannot be combined with other offers, so using the code is the only discount that will apply to that order.
If you do not have a code and prefer an automatic discount: The site wide 20% off subscription sale is the other option. It also takes 20% off subscriptions on the website and does not require you to enter anything at checkout. This is the simplest route if you want the saving applied automatically and you did not receive a voucher code.
If you are deciding between the two 20% offers: Both reduce the plan price by the same percentage on the website. Because the voucher cannot be used with other offers, it is equivalent to the sale for a single purchase where only one discount is available. Choose the 20% off voucher above if you have it and want to ensure the discount is applied; choose the 20% off subscription sale if you prefer not to enter a code and want the discount applied automatically.
If you were hoping to stack promotions or use multiple discounts: The voucher states it cannot be used in conjunction with any other offers, so stacking is not permitted there. The sale is presented as a single offer; there is no indication you can combine it with any other discount.
When you compare the two options for the same plan, pick whichever leaves the lower total at checkout. Because both offers take 20% off the plan price on the website, the final cost will be the same if both apply to the same product and no other conditions differ. Use the voucher at the top of this page when you have it, otherwise the 20% off subscription sale will deliver the same percentage saving without entering a code.