My opinion.
Example 1
I am at a party (or at a club) and I am talking to a girl I just met. She is obviously into me as I can tell by her attraction signals. However I am really tired and I actually want to go home. Should I stay around and continue talking to her for as long as possible (say until closing time)? Or can I “safely” go home and leave her with all the other guys that want to hit on her? If she is consciously or subconsciously showing attraction signals, is she attracted to me enough so she will remember me from then on? Or have I just warmed her up and made her aroused enough for other guys to “grab” her?
Staying with her, in my eyes, would communicate insecurity on my part. If I would be really indifferent, then I would not give a fuck and me leaving her would communicate that to her. However I have had girls “taken” from me like that in the past, in spite of my indifference...
Imo, This is to early to start displaying mate-guarding behaviour. Looking back, I have only started doing mate-guarding behaviour, after I had sex with a girl.
In this example, I think there haven't happened enough things for you to expect that she won't go with other guys and that she will be thinking of you. In this situation, I would maybe invite her, to come with me to another place or maybe to go to mine or her house.
Example 2
Same situation. I am having a conversation with a girl. She seems into me. Another guy or even a friend comes along and starts talking to this girl as well. No problem. However this other guy kind of shuts me out of the conversation. Should I do my best to mingle in this conversation again (pretty needy...)? Should I just stay there (slightly indifferent)? Or walk away and start talking with someone else (really indifferent)?
If a girl likes you, over the other guy. She will give signals to you to stay (or she will come back to you later), or make effort to shut the guy out (like for instance will stand next to you, which on view/postion will make you apear as a team. Thus asif you 2 standing against the other guy. Or she will keep looking at you, all the time. etc. (you get the deal)). So she can continue talking with/being around you; if she doesn't do any of that, then it's a bad sign.
Imo, there is no need to focus on or even think about the guy his behaviour. Just focus on her reaction.
I often find myself in situations like these. I also very often see guys mate-guarding their girlfriends.
Big difference from your examples is though. (I assume most of the time) these guys are fucking these girls already, or are in a (commited) relationship. And in your example, you haven't even fucked these chicks already.
So what do you guys think: Is mate-guarding a good thing to do?
The only "good" things about it, imo are. That the girl feels desired/wanted by you; plus if she thinks you're strong she'll probably feels more safe/protected (from danger/violence/etc). I think it's only suggestable to do, whence you and the girl are in a (commited) relationship and fucking each other.
Shouldn’t girls be mate-guarding me instead of the other way around?
It's agood sign if a girl does that. If you and a girl are in a relationship And she doesn't do (any) of that, it's usually imo a really bad sign.
I must say, I like the reassurance feelings it gives also, it's nice.