*prays this post makes sense, hard for me to put abstract concepts into words*
There's
spam, which is a word typically used to describe the stubborn, haphazard use of the same move/offensive maneuver.
i.e. Your main battle plan consists of always throwing out PK Fire, regardless of the situation, ignoring any startup/end lag, just hoping for a lucky hit so you can do a flowchart grab combo. Sheik camping at the side, charging and throwing needles from across the stage at the tiniest pixel of movement, same for counter characters-- someone spamming Lucina's counter will more often than not use it with the slightest provocation from the opponent (any sort of movement will set these guys off, they're like untrained Chihuahuas). Spammers typically don't adjust their playstyle well when it gets countered.
Then there's "spam" which some people consider the above, but is actually more skillful use of said move. From an opponent/spectator view, this can be hard to identify at first, especially if you're inexperienced.
i.e. You use PK Fire/Counter a lot, but only when it's the best option (and if your opponent is making this your best option a lot, it's gonna look like spam to them. I mean, when I watch Sheik matches it's like 60% Fairs) Players skillfully "spamming" are mindfully using these moves (they are very aware of the startup/end lag and will use it more safely) and the "spam" will have an actual strategy behind it, like forcing you into an uncomfortable position or changing your playstyle (or this same move just strings into itself!). Once you learn your lesson from a few well-timed counters or needles, you start to jump back and rethink your approaches.
"Spam" can also be used to condition your opponent. Do Ness Dthrow>Fairs a couple times, third time you empty jump to bait an airdodge, punish that.
I
f it works, do it. If your opponent is letting you get those PK Thunder juggles, by all means, do it until they work around it. Are they being reckless with their laggy attacks? Telegraphed dash attack? Punish them with PK Fire>choice followup.
All in moderation, though. Stale moves will end up hindering you if you're overzealous, as well as predictability. And being annoying.