Well, one point could be that with an addon you could easily spam-click your drum button to activate it once the cooldown is near the end, and it wouldn't spam the party chat or whisper the next person 40 times.
Another thing to note is that "/in" is defined by AceEvent-2.0, so if you don't have any Ace2 addons, your macro won't work at all.
Yes, the spam issue is exactly what led me to write a smarter macro for the Tainted Core in the Lady Vashj encounter. Pisses me off to no end when some idiot mashes his button for something and spams the same line 100 times in raid chat without ever actually using the action/item he wanted to use. I generally never use macros that indiscriminately send chat messages every time they're activated, and am thankful for AuldLangSyne for giving me notes on ignored players so I can remember is on my ignore list for spamming raid chat with dumb macros. :)