For me, meeting before sex isn't a big deal. XIV is a lot more of casual sex guy than a relationship guy, (mostly because he is really really picky about who he is in romantic relationships with.... much less so who he sleeps with
However, it would be important to me for a physical meeting to take place (unless it's an ldr.... then a phone call would suffice) before it got too serious. I have a couple reasons for that... a lot of the same already posted, (confirm they know I'm not going anywhere, that I'm not crazy, relieve fears on both sides, etc) but for me personally, I have a really good, accurate intuition about people, and I want to make sure I get semi good vibes off of them. Specifically before they spend much time around my son and at my home... but also because they will have a peace of the heart of the person I love so freaking much it's crazy, and I just want to confirm for my own sanity that they aren't demons in disguise. Nervous is fine, of course... I'm looking for creeper vibes primarily.
We don't have a veto, (except in terms of physical or emotional abuse) so even if someone gave off really gnarly vibes, I would explain to XIV what I felt, but he's a grown up and if he wants to be in a relationship with that person, that's fine, it's his call. However, I know he takes my impressions seriously, and I take his seriously as well.
I've never been in a situation quite like this before, but it is a firm line for me. Before he gets too emotionally vested (by his definition... not mine) I want to meet them. I have faith he will tell me when that time comes, and not a moment before