Ancillary services are just the ability to unbundle particular services from your ticket price. This gives you an incredible amount of freedom when it comes to creating a personalized trip of your choosing.
Ancillary services can be thought of like an a la carte kind of air service. Instead of getting a single ticket price that includes a meal, the seat of your choice, your bags, and everything else, the rise of ancillary services unbundled these things from the base price meaning that your ticket price became far cheaper whether it was for corporate travel or leisure travel.
Now you have an option about whether you wanted to include a checked bag or seat preference – by unbundling these services, it allowed individuals who didn’t care about these to save money on every flight they took.