Every tennis player has their own comfort zone concerning racquet head speed. There is a tendency to swing too slowly or too quickly during an actual point in a match.
If you are trying to make sure your shot lands in, or are attempting to be "careful", your racquet head speed is likely to be slower than the optimum speed for your shot. If you are trying to hit a winner or get the ball back to the opening on your opponent's side of the court, your swing speed is likely to exceed that comfortable speed. It is not necessary (or recommended) to swing exactly the same speed each time.
However, if you can keep your shots close to the same speed, your timing will improve and your swings will likely be more fluid. Swinging too fast or too slow can also change the swing path and create more errors.
If you rely on being a consistent player who makes a lot of balls and tries to wear down your opponent, try to emphasize the smoothness of the swing with early preparation and a nice long follow through. If you are a more aggressive player who likes to pressure the opponent, keep your backswing relatively short and remind yourself to accelerate the racquet on the forward swing.
In either case, remember to find that comfortable speed and stay close to it, especially during "crunch time". This will give you the best chance to execute your shots and control the direction and depth that you are trying to achieve.