I have noticed that most times people pour alcoholic drinks especially spirit drinks on the floor before drinking. I want to ask if it's compulsory to do so and what is the rationale behind it before drinking. I noticed that this is even common with Yorubas

Calling upon the ancestors to partake

It's a traditional practice called libation in which an unknown god/idol is being appeased with the drink. More like.. first offering a drink to the gods.

I'll advice you not to join in the practice because you don't know what they are serving/ pouring libations to or what you'll be inviting into your life with such practice.

You no dey mash people head ni?

The gods will wait like mad if they are expecting me to pour my drink on the floor for them, they should hustle and get theirs also

The idea is to reduce the amount of alcohol that will go into your system.

You can also pour offering to your creator, nothing spoil.

ajilegend:
I have noticed that most times people pour alcoholic drinks especially spirit drinks on the floor before drinking. I want to ask if it's compulsory to do so and what is the rationale behind it before drinking. I noticed that this is even common with Yorubas

To appease the gods now.

it's inconsequential. Has no meaning to it except if you want to add your own meaning

Chop alone and die alone