I've found that it really depends how far you are from the first enemy. In a 1v1, there's always at least 4 jumps between your HW and your opponent's HW, often more like 6 or 7: in that case, being able to colonize key planets is pretty important, so I always build 2 civic labs initially so I can get terran population upgrades and ice/volc colonization if I need it. You'll have time to colonize more planets and build the military labs you need later.

In addition, when you have that kind of space to expand, you should be depending much more heavily on scouts as your early-game fleet (before you meet the enemy), instead of anything like LF or LRF - and scouts don't require any military labs at all.

In more cramped games, such as 4v4 and 5v5, you'll be much closer to your opponents - they'll often be only 2 or 3 jumps away from your HW. In this situation, being able to create a decent fleet early on is extremely important: building civic labs in that situation is almost certainly suicide against an experienced opponent.

If there are alot of LRF around LF dont last too long, in recent patches the got a buff vs LRF so they do alright.

I wouldnt make a fleet of LF alone, but with in a mixed fleet. LF bring alot of support, damage and ability wise.

Their speed is great to catch carriers hanging out near the edge of a battle or gravity well.

Also when in fleet battles if your enemy (or AI) isnt focus firing on your caps, LRF naturaly target LF. So they can be used as a meat shields for your caps. If your enemy is focus firing on your Caps then LF will be able to hammer their support ships (flak, support cruisers,carrier cruisers)

I might be in the minority but I highly highly suggest incorporating some LF into your fleets.

I've been thinking about this a lot lately: if your enemy has a whole lot of LRF in the early-middle game (100+ supply worth, which isn't uncommon), is it still worth building a few LF if they'll only survive for around 20 seconds on the battlefield? Or, so that they would survive long enough to deal some damage against enemy heavy armor frigates, would it be worth building more than a few, meaning that a greater proportion of your fleet is more easily destroyed by the enemy? What I'm thinking is that the more you can keep your fleet from being at an armor type disadvantage, the better.

Assuming that the game hasn't progressed to the stage where lots of heavy cruisers and carriers can be produced...

I think what really matters in this consideration is whether the enemy has heavy armor frigates that definitely can and should be taken out pretty quickly at the beginning of the battle, such as repair cruisers and Subverters. Everything else with heavy armor (like flak) I don't think is worth building light frigates for, at least if (while) your enemy has a lot of LRF still in the fray, because your LF would die too easily and wouldn't do all that much to reduce the enemy fleet's damage potential. In comparison to LRF, using your LF to kill those enemy frigates gives those LF a double damage bonus (LRF do 75% damage compared to 150% damage done by LF) while only suffering a moderate reduction in defense (enemy LRF would stop targeting your LRF (100% modifier) and would start targeting LF (150% modifier)).

So, maybe I should use only just enough LF to ensure all of those high-priority heavy armor targets are dead. The more LF than that I have, the more the enemy fleet has a damage bonus against my fleet (with me gaining less in return, if I'm on to killing flak - large hulls, and not quite as important to kill). The more I can keep their LRF's damage advantage to 100% instead of 150%, the better.

As for building more LFs to act as a meat shield for my capital ships... I don't think that's a great idea, at least not with how I play. One should be able to get a cap out of the battle before it dies if you're paying close attention - if enemy LRF attacks it, it will take the cap out of commission for a couple minutes for repairs, but in exchange, maybe 6 of your frigates will continue to live. If I can get 2 capital ships up and running, I'd prefer for them to act as the damage soaks if possible, because they are almost always able to retreat without being destroyed, and if one has to retreat the other can stay behind to soak up experience. I think it's better to take a damaged cap out of the fight than to lose a bunch of dead frigates.

Just my two cents. Losing ships is bad, and killing enemy ships efficiently is good, and after the important enemy cruisers are dead, LF are subpar for both of those goals. (if the enemy has a bunch of LRF) But having a few LF at the beginning is still a good idea if the enemy has those high-priority heavy armor targets.

I've lost a planet to hostile enemy culture, and suddenly my home planet's at 50% loyalty.  How do I fix this?  I've thought about putting public hot tubs on all of my worlds, but there's no icon...

You need to counter by spreading your cultural influence, meaning broadcast centers, also if you park a couple of Capital ships in orbit, they will counter as well until you build said centers....  

Thank you.