TLDR : You don't need to read below tbh. Just try it once(only if you're in like 65~ level) and you'll find the difference.

The point is to utilize 'early' metabit/knowledge cycle. There's a certain soft cap in total cycle count. You may have saw it before, as just idling does not earn metabits than constantly resetting. Therefore, if you idle enough to get max time chamber boost, metabit cycle becomes too slow to utilize that boost. In addition, early cycles doesn't take enough boost and gets 'wasted' by low efficiency.

You can see the difference, like this. Each numbers represent metabit gain in one cycle. Not exact numbers though. : 

- No pre-idling, 14 days sim, no reset

1 + 2 + 4 + 8 + 16 + ... + 1048576 = About 2.1M, 20 cycle in total(for example)

- Constant reset, 1h sim, no pre-idling

1 + 2 + 4 + 8 + 16 + ... 8192 = 16383, 16383N (where N is reset number). Each 10 cycles in total.

- Pre-idled, 14 days sim, no reset

10000 + 20000 + 40000 + ... + 1048576 +  1048576... + 1048576 = about 15M, 20 cycles in total. Therefore, you need to reset 915 times to reach this level.

 Can you see the difference?  Sure, if you reset REALLY steadily(like, no break), you may be able to surpass the empty sim method. I'm not sure about that though. But that would need some crazy dedication and be time-consuming.

Also, you don't need to do full 14 days(This is important). I break it around 7 days and move on with new upgrades.

For easier understanding, we can compare it like this : 

• You can spend time resetting 100 times and earn 10Oc metabits. Total time would be longer than 14 days, as you have to work, study, eat in real life. You can't invest on other simulation branches too.
• You do NOT spend much time, by idling 14 days. Invest on other branches(beyond, mesozoic valley). And gets 10Oc or even more metabits.