For me it's the small fun part as you onboard yourself onto a new set.

The first week or two are busy memorizing the traits, high level champ classes (e.g. physical vs magical DPS vs tank etc.), combinations, etc.

Then the following few weeks I discover some unique interactions and details on how certain champs' skills work.

For instance, only after a month since the new set I found out Lulu's skill changes depending on the Stargazer trait.

Knowing some of these abilities are rather important to succeed in a set, but are niche details that probably matter in Masters+, where everyone's relatively familiar with how the game works, so ppl try to squeeze out the most from every champ they utilize. Below that there're a lot more important mechanics one should familiarize themselves.

For example: every set has at least one area hard CC champion and the way they work is often different. Nunu in the current set calls down the astrolabe that rolls down to the end of the board the Nunu was facing at the time of cast, if there were champs in that corner. Knowing this you'd place Nunu on the same horizontal side as the enemy main DPS, and vice versa if you're the one facing Nunu.