CInt does a whole lot more than Integer.Parse.
CInt will first check to see if what it was passed is an integer, and then simply casts it and returns it. If it’s a double it will try to convert it without first converting the double to a string.
See this from the help for CInt and other Type Conversion Functions
Fractional Parts. When you convert a
nonintegral value to an integral type,
the integer conversion functions
(CByte, CInt, CLng, CSByte, CShort,
CUInt, CULng, and CUShort) remove the
fractional part and round the value to
the closest integer.If the fractional part is exactly 0.5,
the integer conversion functions round
it to the nearest even integer. For
example, 0.5 rounds to 0, and 1.5 and
2.5 both round to 2. This is sometimes called banker’s rounding, and its
purpose is to compensate for a bias
that could accumulate when adding many
such numbers together.
So in short, it does much more than convert a string to an integer, e.g. applying specific rounding rules to fractions, short circuiting unnecessary conversions etc.
If what you’re doing is converting a string to an integer, use Integer.Parse (or Integer.TryParse), if you’re coercing an unknown value (e.g. a variant or object from a database) to an integer, use CInt.