Because I took the 2 tests one day apart from each other, I thought I'd share some comparison based on my experience.
Online: 760 Q49 V44Pros: you are taking it in the comfort of your home and in a familiar environment. No travel required and generally you can rest pretty well. During the test, no mask is also a plus. There is also better noise control because you can close the windows (which is not possible in test centers due to COVID-19).
Cons: the unpredictability of what interruptions/hiccups you may experience due to the combination of internet connectivity and proctors. You can do as many system runs as you like, but you cannot predict and solve every potential problem. This was the reason online test was extremely stressful for me, and I booked an offline test immediately afterwards thinking I had bombed my chance. I started out with a few minutes short because the proctor was talking to me to sort out whiteboard issues (my whiteboard fit all criteria by the way). In the middle of reading a passage, I also got kicked out of the system, which had to be rebooted by the proctor and again lost some minutes and concentration. Finally, after the reboot for some reason the video screen was very dark even though I didn't change any of the lighting. For a few minutes I thought they'd terminate the test. Luckily it was resolved. I had mentally prepared myself for potential problems as I read about many others' experiences; however during the test I was still negatively affected. So for anyone taking the online version, I'd really recommend to prep yourself up and have a steady reserve.
Offline: 730 Q49 V40Pros: less possibility of having technical issues (and more chance to fixed it even if you do). More breaks and more test order options.
Cons: depending on location, sometimes long distance travel is required and can take away from energy levels and rest. Noise due to having to keep the windows open. I know they have lots of earplugs/earphones, but for me the earphone gave me a headache so I went without it.
Overall, I'd say any obstacle with offline is predictable and a normal part of any test. I wouldn't think any of them made me under-perform. With online, it can be either very comfortable and convenient or very stressful.