The reason there are holes at the bottom of mugs is to allow excess water to drain from the mugs when washing them.
The drainage holes at the bottom of mugs allow the water to be transported away and drain out instead of accumulating when the mug is upside down in the dishwasher.
The holes in the bottom of ceramic mugs and ceramic travel mugs is also there to to prevent a big explosion in the kiln.
The only way to prevent a big explosion in the kiln is to puncture a little hole at the bottom of each mug.
The choice between porcelain mugs and other ceramic mugs should be made on the basis of suitability.
Porcelain mugs are good choices when durability is not a major concern and an air of elegance is desired.
Other ceramic mugs are good choices when practical, sturdy mugs are needed.