Changing field max size in Studio

Hello, I'm trying to understand the implications of changing the max size of a text field in Studio. Using 7.5 Professional. 
Does the max size property in Studio actually set the size of the field in the database? Or is it just enforcing a maximum size in the UI? 

The reason behind these questions is understanding what's going to happen if I change the max size. If I decrease the max size, and there are already values saved longer than the new maximum, will the immediately be truncated to the new size? If I increase the size, will blank characters be appended to already saved values? 

Thanks in advance for your help!
Megan