Utility is the part of the buy most players cut first and should cut last. Knowing what each grenade costs, what you are allowed to carry, and which ones survive a tight buy is worth more rank than any individual lineup.
The four-grenade cap is the constraint that decides everything else. A full T-side utility load — smoke, molotov and two flashes — is $1,100 and fills every slot. There is no version of the buy where you also carry an HE, so buying one means giving up something. That trade is the actual decision, not the money.
On a full eco, decoys and flashes are the only sane purchases: they are cheap, and they let five players with pistols do something other than walk into rifles. On a force buy the temptation is to spend every dollar on the gun, which produces five players with rifles and no way to take space — the exact situation the other team wants. One smoke and one flash across the team is usually the difference.
Utility is droppable. If you are sitting on money and a teammate is not, buying them a smoke is more efficient than buying yourself a fourth grenade you cannot carry. This is completely standard at higher levels and almost never done below them.
Post-plant and retake. A molotov onto the bomb or a smoke over the defuse converts a round you are not in a position to win with aim into one you win without firing. Those are the throws most worth learning first, and they are the ones almost nobody practises, because practising a site execute feels more like playing.
Most guidance about utility talks about cost, but at full-buy money the binding constraint is the four-grenade cap rather than the dollars. A T-side player with $6,000 still has to choose between an HE and a second flash, and that choice has nothing to do with $300. Work out what your role needs in its four slots first, then check whether you can afford it — not the other way round.
A T-side rifle round with a full kit — rifle, armour and helmet, smoke, molotov and two flashes — is a little over $5,000. That is why the second and third rounds after a won pistol round matter so much: they are the rounds where you can either arrive with full utility or arrive with a rifle and nothing, and the difference between those two teams is much larger than the difference between two rifles.
Dying with utility. If you end a round with an unthrown smoke, it was worth nothing — you paid $300 for a grenade that did not exist. Watch your own demos for this specifically; almost everyone below the top ranks does it several times a half, and fixing it requires no aim improvement whatsoever. Utility unspent at the moment you die is the cheapest improvement available in the game.