I noticed that sometimes I would see holes labelled like this:

but most of the times, they would be drawn "normally", like this: 
Why would someone use a dowel pin symbol if a regular hole means the same thing?
I noticed that sometimes I would see holes labelled like this:

but most of the times, they would be drawn "normally", like this: 
Why would someone use a dowel pin symbol if a regular hole means the same thing?