Not always, especially during debugging when Break On All
Errors is set.

You get your stability by using good error handling procedures. You can learn
about that in VBA Help under On Error.

A Dim statement only establishes the name and type of the varialbe.  It
presists as long as it is in scope.  You assign a value to it in VBA.  It
retains that value until it goes out of scope or you change the value.  You
don't really "Clear" a varialbe.  It will always have some value as long as
it is in Scope.  The default value of a variable depends on it's type.  If
you need different forms to share the same variable, it has to be declared
(Dimmed) as Public in a standard module.  There are also other techniques for
passsing values between forms, but that is beyond the scope of this
discussion.

VBA variables are naturally faster and use less resources,
but, in practice, you will probably never notice the
difference.  As Klatuu said, scope is very important.  There
should be no need to use a text box instead of a local
variable.  The question only makes sense when comparing a
variable declared as Public vs a text box on either the
current form or an always open form.

You place values in either a variable or a form control by
using a VBA assignment statement.