Web User Control in general

I am new to ASP.NET programming and I am reading and browsing example projects.
As far as I understand advantages of User Controls (ascx) are:
- HTML-Controls and Server Web Controls can be "packed up"
- Elements of the Control can be exchanged at runtime through the Placeholder
1) Are there other advantages of User Controls compared with a set of
"standalone native" Controls?
2) In particular, when I am going to design a
site with several labels, buttons and grids, should I design it by HTML/Server
Web Controls, or should I build one or more User Controls?

Thank You