The one issue I have with the suspect flag is that it's a double-edged sword.
On the plus side, you don't get other parties caught in the crossfire.
On the very non-trivial downside, you're going to see one half of a lot of conversations. You're not going to see if the reply to, say, a 'awwwwwyiss that PB is hawt I wanna TS!' sort of page is met with silence, a 'fuck off!', a change of subject (ex: 'I think they suit the look of this character and I've always liked the actor's work, but I didn't choose them because I want to TS with them with anyone ever'), or a 'fuck me now!'
This is often very relevant, and can be hazy as hell when you're only seeing one side of a conversation. Someone continuing to pursue under each of those circumstances has a very different interpretation, and it is not always going to be clear from just one side of the conversation.
Another might be, say, the innocent party saying, 'I have a scene with X but can meet you later' -- super common -- and an observed reply of 'I don't get along with them (notice lack of X being identified here), so I'll see you later.' Outside of context, this can look like a completely harmless exchange -- someone being live and let live re: someone they don't get on with and agreeing to meet up later as suggested -- or it could appear to be something more like 'I don't like that person so see ya later, I'm out'. The latter definitely has a very different vibe. (ETA: Also, with X not being identified, it could be interpreted as part of a bashing routine against someone who isn't even the person mentioned -- or, worse, missed as being precisely that for the same reason.)
So, while it's a handy tool, it is VERY important to be aware of this limitation. Those are just two examples, and I'm sure people could come up with plenty more. We already have a lot of communication issues in this hobby, so this is worrisome in a very real way.