Frequency
Generally speaking...
The less often you train the more precise your training must be and the more intentional you must be (than if you train more often).
Training one or two (to even three) times per week means most of your sessions should work your full-body and include most or all of the body's major movement patterns. This is for ensuring that the biggest ROI, bang-for-your-buck, most impactful structures and systems are hit regularly enough to move you forwards. Most of your sessions should also be fairly full-body because if you are training one or two (or even three) times per week and you miss a day, then you have missed 33 or 50 or even 100% of your opportunities to work the most important progress-drivers — a big and potentially too big percentage of your workload; you can less afford to have sessions devoted to more singular areas because if you miss it you may go too long before seeing it again and you will not be training it enough to drive progress. You can of course absolutely feel better and make positive changes from training one or two or three times per week, but your training (and execution and expectation-management) must be structured appropriately.
Training more frequently (and consistently) means you can afford to have more specific sessions because you are still hitting the biggest players frequently enough. You can focus more energy on more specific tasks, going deeper because you have less breadth for focusing on and more recovery time (intra-session and between sessions) before hitting it again. Missing a day has a smaller impact on your total expenditure. Your accessory work can also be more varied and complementary to reflect this.
You can feel, function, perform, look and or live (you can and or will be) better from any and all exercising (than you can by not exercising), and you can improve more safely and effectively by Training than you can by just exercising. Your training frequency and consistency (among other gym-related factors) determines your training structure and (among other, usually outside-of-the-gym influencing factors) also determines the timelines you can reasonably expect to see certain results.