10% barely has any selling impact because the prospect still has to pay for what you're selling. They get some money off, but they still have to fork money out, and people need to be persuaded to do that.
People mistakenly believe that a small discount has a strong enough impact to convert a sale. In reality, it's nowhere near enough. It can work to a degree if you couple it with other offers in an overall marketing message, but that's about it.
Plus, just how much is the 10%? In B2B, it's often a very small sum of money unless a sale is worth thousands of pounds. I've seen some businesses try to push a 10% discount on a £50 item. Do they really expect £5 to sway prospects from one business to the other?
Free items and offers work because of the perceived value - not necessarily the actual value. £20 is £20, but a free item can be many times more valuable to the prospect. The key is to assess the prospects, assess why they want to buy the original product and then offer something which will really play on their needs. If you do this, then a £50 free item could be worth £50, but a £20 item could be worth hundreds to them. Just imagine the impact of that.
However, if you do take this approach, never neglect the selling of the product being sold. So many prospects are caught out in the situation where they really like the sound of an offer, but they prefer the original product from another business. This is purely down to what has been said about the products in sales copy and marketing material. Offers like these should be used on-top of the existing marketing messages, and should never be used as an excuse to neglect the original selling points.