Difference between 2.0 and 2.0f (explicit float vs double literals)

Question

I had some questions about putting f next to literal values. I know it defines it as a float but do I really need it? Is this 2.0f * 2.0f any faster or compiled any different than 2.0 * 2.0? Is a statement like float a = 2.0; compiled differently than float a = 2.0f;?

Answer 1

Sometimes you need it to explicitly have type float, like in the following case

float f = ...;
float r = std::max(f, 42.0); // won't work; (float, double).
float r = std::max(f, 42.0f); // works: both have same type

Answer 2

I's rarely about speed (at least directly), but the fact that otherwise the compiler will warn about converting double to float.