At the very least not allow the secondary purchasing of all nades (HE, Flash, Smoke).
Limiting the max amount of first purchased nades per team could also be a benefit as well.
Agreeing with what others said above, some CTs will rebuy nades and spam them middle Double Doors at the start of the round to further conceal themselves crossing mid or pushing into lower tunnels. This also slows down the Ts who rush down mid from T spawn. Or CTs load up short A with an over abundance of smokes and flashes to overextend and further delay T's from pushing up Short A. Same goes for upper B tunnels into B. Stagger a smoke from inside B - CT side, one after another and limit the visibility and draw down on time. While this can aid the CTs in delaying the T's, it severely slows down the game for both teams, and is a major hindrance to the momentum and energy to the server in my opinion.
On the other hand, some Ts spam & rebuy flashes and smokes for Long A. The intent is to deceive the CTs into thinking it's a Long A rush, while after the initial toss of the first purchased nades, Ts run back to spawn to rebuy and usually push towards Bombsite B. While I don't agree with the rebuying of secondary nades, at least in this case their usually doing it and following it up with a swift rush to somewhere else - just as the CTs are rotating to the calls of "Long A rush, help! now!". If the Ts follow through on their rush elsewhere, it aids towards their objective which tends to keep the momentum and energy positive for both teams as the game plays out. When T's get bogged down, everywhere, every time, too often it results in them not doing their objective. This leads to Ts not rushing, but rather to play defensively and to spend a majority of the rounds time killing CTs from afar in hopes of a last moment rush to site as the round nears expiration.
Most CTs want the T's to rush them, its fun and keeps things exciting! Usually, the Ts want to rush the bombsite, its fun, exciting, and attempts the objective!
Nobody like stagnation. This slows the game down for both sides, and in my opinion subtracts game enjoyment for both teams.