The sattvic diet is generally considered important if you are engaging in meditative practices.
However, I have to wonder if it really makes a difference for ordinary people. In general it is thought that foods like garlic and onions prompt anger and lust, which is why they are to be avoided.
In Taiwan here vegetarian usually means Buddhist vegetarian and consequently no garlic or onions are added to the cuisine. If you eat at a vegetarian restaurant it means by default none of the five pungent herbs will be used. Anything you buy at the grocery store labelled as vegetarian likewise means no garlic or onions.
Now, granted, this is a little island in the Pacific Ocean. I found avoiding garlic and onions back home in Canada rather difficult. In Japan likewise it wasn't so easy. After attempting a sattvic diet I gave it up as it was proving far too inconvenient and I didn't necessarily see a direct benefit. I was also in a monastery eating a pure sattvic diet and I honestly didn't sense any benefits to it.
The issue of eggs is controversial. Some people see it as theft from an animal, so they refrain from eating eggs. Others don't care.
Among Sino-Buddhists (Vietnamese included) I would estimate that most devout Buddhists would refrain from eggs, but forget about it when it comes to cookies and cakes.