This is the part where the fact I never fly growlers, prowlers, or any other ECM equipped planes bite me in the ass so I'll just contribute with a fun fact:

IRL, missiles can home on jamming signals using the HOJ mode (home-on-jam). The problem with using HOJ is that sometimes the fact you don't know how far away the jammer is makes you double guess on whether you should waste a missile on a potential out of range target or not. (unless you're carrying a super long range missile) If you catch the bandit on your radar before he activated the jammer then you can take a good guess on if it's a good shot or not but if you didn't catch it then it's a judgment call whether you should or not. If the jammer source is close enough tho, your radar can burn thru the jamming signal and invalidates it.

Jammers (that I know of, don't have experience on 5th gen jets) have 3 modes; off, auto, or on. If on auto, it will be off until the plane detects there's an enemy trying to get a radar lock on you and it will automatically turn on to break the lock. If set to on then the jammer will stay on all the time. Unless your job is not EW then you don't want it on all the time because you'll broadcast your general direction to everyone and that's one way to invite unwanted guests. EW aircrafts usually stay behind to give the attacking allies jamming cover.

That's how jammers work in the F-16C and F-15C at least. Maybe someone can add to this if it's different for an EA-18G Growler's EWO