Is using flags very often in code advisable?

Question

I came across lot of flags while reading someone else code,

if (condition1) 
    var1 = true
else
    var1 = false

then later,

if (var1 == true)
    // do something.

There are lot of flags like this. I eager to know, is using flags very often in code advisable?

Answer 1

This:

if (condition1)
   var1= true;
else
   var1 = false;

Is a classic badly written code.
Instead you should write:

var1 = condition1;

And yes, flags are very useful for making the code be more readable and possibly, faster.