What is "grandpa style"?
More or less the same approach as grandpa style when you want your tea with minimal fuss.
It's not grandpa style. I'm not the greatest writer so my description may not sound too clear.
When your tea in a gongfu session loses it's taste you add 1/3 of the original amount of dry tea or less and do short infusions.
In bitter shengs you'll taste less or even no bitterness and just floral aromas or whatever else there is to explore.
Grandpa style you'd just refill a large cup / thermo that contains water and the tea leafs whenever it's water level gets too low. Never tried that so I can't tell you what the result would be.