Here are a few reasons why this could be a very healthy thing to do:

#1. Makes Boundaries Clear

Yellow-carding on the first date or first few dates can be very healthy for a relationship as it makes certain boundaries clear. 

It also allows both partners to ponder if those boundaries are something they can take in a long-term relationship or not. 

This can also save either of the partners from getting blind-sided later on in the relationship and create problems.