Would you like the long answer? Basically there are lots of considerations - but it starts with do you intend to relay the events as per NIP-01, and secondarily what processing or data querying are you performing.

Do you need to reply with signed events?

Can a person react twice?

Can a person react twice, but with different reactions?

Can your processing see the same event twice?

Can someone delete a reaction?

If you identify a spammer of fake reactions, if you’ve compressed the data, can you filter them out now - or impossible?

Fair few more cases to consider in addition to those as well. Decentralisation is complex. Blockchains don’t fix almost any decentralised problem.. so some areas are new and unsolved CS (or un-applied.. we have solutions that haven’t been battle tested yet).