@OP, what perspective are you asking? In all game modes, 1s, or 4s?
In 4v4s, I often have to get grenades before CPT or LT simply because it is viable for ostheer to get 2-3 MGs if the other player gets 3-4 volks. Smoke can be vital for winning those early game engagements. In 1v1s, Nades are usually a mid game tech. Smoke Nades are good against enemy MGs, against tanks (USF smoke nade slows tank movement and disables main gun), and enemy LMG units at range (high vet grens in mid game, Obers). Using regular nades are, more often than not, not worth their price. for 2 nades you can get a BAR. Nades work better in the late game when your opponent is fatigued, against weapon teams, against low health squads, etc. Throwing grenades
behindcover can also earn you wipes, but only do this if you see your opponent dodging nades, or if you know he's good.
As for bazooka and BAR tech and not teching, in 1v1s, there's a few ways you can approach this and they differ slightly from 4v4s.
As Skabinsk said, if you're floating a lot of muni, you want to research the tech so you can get that extra dps and beat volks, beat LMG grens. While he (judging by his playercard) tends to play lots of 3s and 4s, and prefers BARs, in 1s it's a bit of a different ball game on your own. Infantry Company and Tactical Support Company are both good because they have the M1919. The M1919 lets you win engagements at long range against volks grenadiers, and against grenadiers. in tandem, they can beat Obers as well, depending on micro, vet, health, etc. The BAR is a good mid range weapon, used with a flanking squad. In any case, BARs and M1919s will increase the dps of your riflemen. You've just got to decide what role you want your squad to play in the grand scheme of things.
That being said, in 1s and 4s I find Tactical Support and Infantry Co. are my most used commanders because of the LMGs, in 1s, infantry because of the mines/sand bags, in 4s, tactical support because of the potency of the callipoe. Thus, I usually have access to M1919s.
Putting M1919s on all of my rifles/squads gives me less things to micro, but mixing m1919s and BARS on different squads can really pay off. Typically, my build order is RE Rifle Rifle Rifle LT M20. You can also get 3 rifles and captain, or 4 rifles and captain. The RE at the beginning gives you a slight advantage in capping power. You can also put the 2nd RE squad in the M20, giving yourself an extra zook. Hector does this in his 1v1 armor co. strategy, then getting an extra bazooka on that squad, supplementing his subsequent captain tech.
http://www.coh2.org/guides/47115/armor-company
That's more of a build if you're fighting OKW Luchs or maybe Stug III E from Ostheer. You can do that late game as well in 1s. Zooks still pen medium armor and can tip tank engagements in your favor.
That being said, getting the bar/zook tech can help for your AT. If you grab one extra zook on your M20 crew, then go captain, you've got 4 zooks, 3 for free, and you've got quite a strong mid game in terms of anti infantry and anti tank firepower.
When it comes to BARs/M1919s, double M1919 LMGs will beat volks. If you've got 3 or 4 rifles with M1919s, you can beat obers, you can beat Grens, you can easily kill out of place MG42s/34s. One thing I like to do is put M1919s on one RE squad and 2 riflemen squads. ON the REs, this allows you to use your suppressive volley fire ability at range at minimal risk to the REs. On the two riflemen, this allows you to have long range dps squads that punish pioneers, assault grenadiers, sturmpioneers, or falls that are coming at you over open ground. I put BARs on the other two riflemen squads. These guys get into mid range, they go into the VPs and cap them under enemy fire. With 5 men, they're durable. With the BAR itself, they've got a lot of dps. They're first in line in most of the engagements. They're being covered by the 3 M1919 squads behind them; those M1919 squads are firing smoke nades first, in front of the MGs, or in front of the LMG34 Obers, allowing the BAR'd rifles to close and get into cover.
I do this all the time as USF. In 1v1s, the mine ability is great for shutting down flanks by infantry or vehicles. If it's 40 minutes into the game, you can park your M20 in your base, then have a squad jump in it and plant a few M20 mines on a side of the map that you just capped.
Long story short, always get BARs or M1919s. It's best to mix them up in your army, but not on a squad to squad level. Use smoke nades when you need to in the early/mid game, definitely in the late game. Build a muni cache or two. Use grenades sparingly. Always use your munitions. Use your M1919 and BAR squads together, in an intelligent way. Identify your biggest threat (suppression platforms, charging squads... armor?)