Welcome Hodge!
As you can see by the responses, it is all about letting the wine have some oxygen at the start.
As you watch your first kit you will see the yeast really takes off and puts out a lot of CO2 gas. That CO2 has a lot of oxygen in it (2 times as much oxygen as carbon) - so when the yeast is very active you feed it oxygen by doing a daily or twice daily stirring. It doesn't make much difference if the lid is snapped on or not at this stage because the bucket will be full of CO2 anyway, but it iscritical to make sure fruit flies and other things cannot get in and you want to hold that CO2 on top of the wine so it doesn't get too much oxygen.
At the end of fermentation when the yeast slows way down and can't use much oxygen, then you isolate the wine from anymore contact with the air (oxygen). It will still be gassing off trapped CO2 for a while, so you can move it out of the bucket when fermentation is done or almost done and still be ok.
When fermentation is complete you must, must, must protect the wine from oxygen.