If you want to add reps and/or weight to get stronger over time you need to have a plan on how to progress. It's very common to increase weight by 2,5kg increments for compound movements like squats, deadlifts or rows because 1,25kg plates are usually available in every gym. Increasing weight by those increments is fine most of the time, but even 2,5kg jumps can be too much if you're looking to progress long-term on an exercise.
Getting stronger takes time. It's not uncommon for myself and clients to make baby steps over MONTHS, slowly adding weight and reps and building strength like that. Past the beginner level that's how you grow. Adding 5kg to your squat every week is not happening anymore.
So 2,5kg jumps may be fine for big lifts, but what about isolation exercises like curls? Here's two examples to illustrate that you have to use smaller increments to keep progressing on smaller joint movements.
Example 1 (Compound): You currently squat 130kg for 8 reps and want to add weight. You choose to add two 1,25kg plates and therefore add 2,5kg to the bar for your next squat session.
Example 2 (Isolation): You currently curl 40kg for 8 reps and want to add weight. Just like you did with your squat, you want to add two 1,25kg and start curling 42,5kg the next training session.
Clearly, this is going to backfire. You're trying to progress by adding the same amount of weight to an exercise that uses much less muscle mass. This will inevitably lead to progress stalling and you getting stuck with that big weight jump.
Adding single weight plates to cable stacks, using microplates for dumbbells or attaching weight plates via lifting straps to your wrists for exercises like dumbbell presses or laterals. You can always progress, you just have to custom fit the increments to each exercise. The less muscle mass involved in an exercise (e.g. curls compared to squats) the smaller the percentage should be.