Is it important for plants to be transplanted from smaller to bigger pots?

I am wondering as I see this all over internet,but why?
When you plant it outside it grows bigger and healthier and it is not transplanted 2-3 times as some would say it is important to do so,so why wouldn't I plant it straight in 5 liter pot when indoor?

it lets the root grow in stages and give the plant a solid foundation ive found. it also seems to give them a boost.

Transplanting is only important if you want bigger growth,the same plant in a 5 gallon bucket would grow more than it being in a 1 gallon bucket.
And 5 liters is cool to start and finish if you plan on having small plants like me.Next year I'm using either 30 gallon totes or 39 gallon garbage cans
started inside and wheeled outside.

I transplant once to my finishing pot once mine are (from seed) large enough to deal with it. Then I let em ride.