In Team Fortress 2, after a player dies they will respawn in a certain amount of seconds. The respawn time is different based on what mode, map, as well as the current state of the game. Generally, the attacking team’s respawn wave will be faster than the defending team.
When you die, you will be placed into the next full respawn wave. This means that if you die now and the base respawn wave is 10 seconds, and the next respawn wave is in 4s, then 14s, then 24s … you will be placed into the 14 second respawn wave, meaning that your respawn will be from 10 to 20 seconds after the deathcam. Note that when a team has less than 8 players, the respawn times are automatically scaled down.
Valve on the TF2 blog has listed some of the reasons on why they chose this system, including that respawns pace the game’s flow and prevents fatigue. By grouping respawns into waves, players will be spawned into squads and this tends to promotes teamwork even across strangers. Without respawn waves, game modes like Attack/defend on the last control point will become unbalanced as it will be harder to capture the last CP when as soon as you kill an enemy they can come back out again. Servers that have enabled instant respawn therefore unbalances the game and tilts it in the defending team’s favor.