Primary with or without airlock?

at my local home brewing supply stores they all recommend that i use a primary with no airlock and just put the lid on top and let it ferment for the first 4-7 days in there and then transfer it to the carboy. but lots of places i read say to have a primary with a hole in the lid and put the airlock in there. is this latter method better if you let the batch sit in the primary for weeks and bottle out of there? i dont understand why both methods are often said to be used but i have never heard anyone talk about the differences between them. any information on this subject would be greatly appreciated.

I primary with aluminum foil on carboys, loose lid on buckets for about 7 days, then clamp down/add airlock. After that I wait about 1-2 more weeks before transfer to kegs.

Many folks just cover their fermenter buckets with a piece of plexiglass letting the co2 push out between where the plexiglass and the bucket meet. Others cover their carboy mouth with tinfoil.

An airlock is just a vent to release excess co2, so as long as you have some way to let the co2 get out without letting oxygen in, any method works.

Even loosely putting your grommetless bucket lid will work.

The common and easiest way is with an airlock, but many folks put too much emphasis on whether or not their airlock bubbles, they think that if it's not bubbling something may be wrong, when in truth it's just a matter of need. If there is so much co2 building up that it needs to vent, it will. If it gets out some other way, beer will still ferment just fine.