Perhaps one of the biggest issues that plague FPS-games are cheaters.
If you use a server-authoritative model, you will prevent some level of cheating. But why do this if people can still aimbot?
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There are turnkey solutions for cheating, involving the equivalent of antivirus scanners specific to cheats. This is only cost effective for games that plan on having (or are aiming to have) an ongoing competitive community. Beyond that, you can incorporate fuzzy heuristics on the player's movement and aiming inputs to differentiate between natural and unnatural behaviors. Whether it is 'worth it' to you is primarily based on the time you wish to invest and your level of experience doing statistical analysis on streams of data; if you're learning from scratch, then it is probably not worth it.