One of the gripes I've more frequently about 5th ed is wound allocation. Nob bikers, TWC, wolf guard, etc. There's not much you can do about it in CC (usually where these guys end up) but you do have options in the shooting phase to counter-act their advantage.
Say there's a 5 man(?) Warrior unit with VC and a Prime holding an objective in cover and a sternguard squad with 3 combiflamers and 2 heavy flamers toasts them with all they've got. depending on how the wounds turn out(of course) the Tyranid player could allocate the ap 4 shots alternately to the VC, who would die, and to the prime, who saves on 3+, while taking the AP5 shots on the warriors 4+. Had he only fired the heavy flamers, only the prime would've made saves; everyone else touched would've been wounded. Alternately, had he fired the combi's first, and the nid player took saves before the heavy flamers went off, he would seriously short-change himself in terms of saves. It's therefore very important to
a)not take saves as he makes wounds
b)expect the same.
Maybe its only a local problem but it could change your game.
Which brings me to the title. Sometimes you have to hold back. If you want those ap2 shots to do damage, then think twice before firing your bolters. It seems counter-intuitive, but it becomes almost second nature after one gets used to the system.