Promotions can rapidly cause major problems when they overlap, as it creates many more possible options as to what rules should be applied.

For example, if you have a buy two 'A' and get 'B' free in a store that also has buy two 'A' and get 'C' free, you are effectively giving both B and C away when the user buys two of 'A'. Other problems can occur when one of the 'free' items (B or C) in the case of the above, also earns some promotion discount. For example, if you had another promotion buy B get D free, then the item B (which is free thanks to one of the promotions above) also results in a free item 'D'. So the purchase of two 'A' now gives B, C and D for free. Probably not was intended when each promotion was created.

To limit the chance of multiple promotions, stores may wish to limit the total number of promotions that can be triggered in a single order. The config setting frontend.promotions.maximum can be set to zero for 'no limit', or any number above to limit promotions.