When you create a group, Recharger creates three "don't recharge" rules by default for each entity in the recharge group. One rule for revenue account code transactions, one for expense account code transactions and one for balance sheet account code transactions.
As every transaction from Xero feeds into Mayday, and every transaction needs to be matched by a rule, by default we're saying don't recharge. You then create rules for your recharge situations which supersede the default rule.
You will likely want the default rule to be what happens to the majority of your expense or revenue transactions. In most businesses, this will be “don't recharge” but there are certain situations where you might want a rule that does recharge those costs or revenues to be the default.
For example, if you have a transfer pricing policy where the cost centre entity cost plus recharges all (or close to all) of its costs, you can set this to be the default.