For general fitness/conditioning, probably not necessary and especially not if you do 2 hours of calis or calis classes weekly along with your 2-3 hrs/wk of mostly powerlift work.
What are typical accessory weight exercises? Things like curls, calf raises, cable pulls and pushes of all sorts, leg press, lateral raises, leg curls, and many gym machine activities which target specific muscle groups.
Typical compound-movement powerlift work (deadlift, rows, pullups, barbell squat, military press, bench press, maybe dumbbell lunges) strengthen pretty much all skeletal muscles - and your core too- and are more functional than isolated muscle exercises. (Most people do not do Olympic lifts but if you want to try them, go for it. With a coach, please.).
There are a few exceptions. 1.Beginners often need accessory exercises for a few months before moving forward 2. Some accessory exercises can help ramp up your powerlifts. For example, I work on overhand curls and kettlebell Farmer's walks for my grip strength because that can be a limiting factor for my deadlifts. I have weak forearms. 3. Another exception is for bodybuilders who choose to focus on developing good-looking specific muscles. (That's not really about functional fitness, though - more about looking great naked.)
We stand by our Fitness For Life recommendations for women and men of any age: 2-3 hours of mostly heavy weights, 2-3 hrs of calisthenics without heavy weights, about two half-hours of HIIT cardio, 1 hr of endurance cardio (replaceable with a 5-6 hr hike, bike ride, etc). Not counting hikes, a total of 6-7 hrs/week is sufficient - but no less than 2 hrs of real lifts with some accessories if needed to complete the hour)
