It is called "anticipated separation" which is perfectly fine for both departures and arrivals.
FAA Order 7110.65W:
3−10−6. ANTICIPATING SEPARATION
a. Landing clearance to succeeding aircraft in a
landing sequence need not be withheld if you observe
the positions of the aircraft and determine that
prescribed runway separation will exist when the
aircraft crosses the landing threshold. Issue traffic
information to the succeeding aircraft if a preceding
arrival has not been previously reported and when
traffic will be departing prior to their arrival.
EXAMPLE−
“American Two Forty−Five, Runway One−Eight, cleared
to land, number two following a United Seven−Thirty−
Seven two mile final. Traffic will depart prior to your
arrival.”
b. Anticipating separation must not be applied
when conducting LUAW operations, except as
authorized in paragraph 3−10−5b2. Issue applicable
traffic information when using this provision.