If you're going to powerlift, treat it like a sport. You need to be fit enough to play a sport, powerlifiting is no different. However...
Powerlifting is unique in that it revolves around performing lifts that would be otherwise used as a form of physical preparation in other sports. The squat, bench press and deadlift are all lifts that are commonly used in sports like football and hockey to increase upper body and lower body strength. As a powerlifter though, your success depends on your strength on these big 3 exercises.
Ask yourself: Are you in a position to practice the powerlifts with a high frequency? Or can you perform other exercises and round out your athletic abilities while still achieving similar progress?
Just like how athletes must be fit and strong enough to play their sport, powerlifters must be fit and mobile enough to perform the powerlifts. Many times, I see beginner powerlifters neglect all forms of general physical preparation - cardio, intervals, core work, improving overall movement quality, etc. Only until the novices have run Sheiko or Smolov, do they realize they're not cut out for highly-specific work just yet.
While I'm aware that trainees must practice the powerlifts frequently to become a better powerlifter, I'm a big believer in cross-training and including training variation when needed. The skill requirements for raw powerlifting are relatively low, compared to other strength sports such as Strongman events or Olympic weightlifting. Paired with the fact that there are many exercises that can mimic the powerlifting movement patterns, training variation can be very useful.
My clients who have had a history of playing multiple sports or clients who perform a wider variety of training (cardio, unilateral training, core training) in the off-season have been able to become more resilient to injuries, as well as be more successful when it comes to physical performance and mental health on the powerlifting platform.
Mental health and training monotony are big concerns in powerlifting as doing the same exercise over and over again can mentally bog down a trainee. If training isn't fun, why train?
In the last couple of months, I've seen powerlifters wanting to branch out and try different training modalities like Olympic weightlifting and calisthenics, its a great thing to see. Athletes almost always gain some perspective and learn a few things to apply to their own powerlifting training.
Offering some solutions
For novices and intermediate lifters: I urge you to do your fair share of general physical preparation. This means picking exercises that widen your athletic base, while keeping a degree of specificity as you want your physical attributes to transfer over to the sport of powerlifting.
These are my favorite exercises to include for overall athleticism (in no particular order):
Occasional long-slow steady state cardio workouts - FOR RECOVERY
Anaerobic cardio intervals on the assault bike or row ergo machine (60-90 seconds hard, 60-90 seconds easy, alternate) - FOR GENERAL WORK CAPACITY AND HIGH EFFORT TOLERANCE
Isometric core exercises to build core stability and strength, practice bracing and breathing techniques (RKC plank, pallof press variations) - FOR CORE STRENGTH AND STABILITY
Unilateral training (split squats, 1 legged RDLs, alternating dumbbell presses, 1 arm presses, etc) - FOR SYMMETRICAL STRENGTH AND IMBALANCES
For more advanced powerlifters: you've probably addressed general physical preparation properly, that's how you've progressed to become an experienced, advanced lifter. Variation can still be included. Aside from the powerlifting-specific variations, exercises that mimic the movement patterns of the powerlifters can still be used:
Squats - Quad dominant squat pattern
Bench Press - Horizontal Push
Deadlift - Posterior chain hip hinge pattern
Possible variations to use as accessories, during deloads, or in place of the big 3 when training around injuries.
Squats and deadlift alternatives (Front loaded squats, trap bar deadlift, prowler pushes, squat jumps, olympic lift variations)
Bench Press alternatives (weighted pushups, neutral grip presses).
Occasionally including these into your program can reduce the chance of over-use injuries and can be used as alternative exercises to perform around nagging hip and shoulder injuries. Exercises like the neutral grip presses can relieve shoulder stress, while trap bar deadlifts can still provide a high-intensity stimulus without taxing the lower back to the same degree as competition-style deadlifts.
Know when to specialize
Pre-competition is the best time to reduce the amount of variation you're doing, and ramp up the intensity and specificity of lifts. During this stage, the frequency of the competition lifts increase and unnecessary stressors that have already contributed to our athletic base are removed. Things like cardio, isolation exercises and most "bodybuilding" accessories start to decrease in volume in preparation for the higher intensity squats, bench presses and deadlifts.
Understanding training residuals are particularly important when it comes to peaking for a meet. We know that high volume training is required for hypertrophy, however, when it comes to maintaining that muscle mass, lower volume works - as long as intensity and effort is kept high.
This means that as you spend more time with the intensities 85% and above, performing 5 reps or less, you'll still be able to maintain that muscle mass. As a result, it is not necessary to implement "hypertrophy" days in hopes of building muscle, especially if a hypertrophy-focused phase has already been performed in the preparatory period.