Is it actually healthier to sniff phlegm / mucus back IN the nose (in general, i.e. apart from when you have a cold etc)?

I recently had a cold (possibly flu), unfortunately, due to some extreme / 'too much too suddenly' health fasting combined with cold weather and not much exercise or probiotics or a few other things I should be doing, all at the same time, and it lowered my immune system enough to get under the weather, despite eating generally super fresh / healthy foods (mostly vegetables, fruit, and some bread, all organic, nutritiously grown and generally picked on the day it was eaten. I know. I'm embarrassed.).

Long story short, I let myself get chilled (very much), and just wasn't eating enough (or exercising) for my body to take it like it normally would. I learnt my lesson.

While sick, I did some research on the relationship between 'getting a chill and contracting a cold/flu'. I came across interesting info that mucus, is actually a healthy thing and is supposed to line your various inner walls (like throat, I think stomach, and probably many other places), to PROTECT you from things like pathogenic viruses / bacteria etc. It's a natural PART of your immune system in PREVENTING and FIGHTING diseases in the first place, and I read that if you have a totally dry nose, that can actually make it EASIER for various bacteria and viruses to enter your system and generally cause trouble to your body, and so I concluded that a WET nose seems to actually be a good thing, if you can not be bothered by it. It was very interesting to learn.

So I now ask and wonder, unless you genuinely have excess phlegm that would indeed hamper your chest's ability to breath well / have serious amount being produced etc, do you think it's maybe a good health principle to NOT reach for the hankie but just generally sniff that phlegm back down your nose, if mucus seems to be so useful for immunity? Like e.g. when it's cold your nose tends to go a bit runny, things like that.

Or is the phlegm that makes its way to your nose not actually that useful in protecting from nasties (unless maybe you HAVE the cold)? (I think it might be, from that info of dry nose being more susceptible to them.)

What do you think?

N.b. I already have a diet and lifestyle that doesn't produce much nose phlegm, such as no dairy, meat, etc...