The earlier commit always used the dimension from the customer branch to dimension customer payments so there was no need to specify dimension on the customer payments page.

The recent commit was needed to handle a special case where a customer was invoiced separately by two separate dimensions of a company but the customer paid both invoices with a single check, so dimension was added to the customer payments screen to split the payment to the proper dimensions.

The purpose of these commits as stated in the original pull request, is to keep A/R correct when tracked separately by dimension.   If one does not need to track A/R separately by dimension, FA works correctly without these commits.

@braathwaate's commits that partakes of his custom functions are also worth a look.