Basic Competence

[Iyrnwaen]

But it's usually not a good idea to have the team sitting on the checkpoint.

No, it's almost always a good idea to stack 5 on the point for a quick cap after you win the first engagement.
Cap speed is based on how many players you have on the point vs how many enemy players are on the point.
If you have 5 and they have 0, the point caps in a few seconds. If you only have 1, it takes forever and can be solo contested.
If you have 1 on point, 1 or 2 standing near the point but not on it, and 2 or 3 running around trying to pick off stragglers,
you're creating an opportunity for your own people to get picked off or for a single opponent to freeze cap progress,
and you're giving the enemy team loads of extra time to regroup and contest.

[Gserpent]

No, it's almost always a good idea to stack 5 on the point for a quick cap after you win the first engagement.
Cap speed is based on how many players you have on the point vs how many enemy players are on the point.
If you have 5 and they have 0, the point caps in a few seconds. If you only have 1, it takes forever and can be solo contested.
If you have 1 on point, 1 or 2 standing near the point but not on it, and 2 or 3 running around trying to pick off stragglers,
you're creating an opportunity for your own people to get picked off or for a single opponent to freeze cap progress,
and you're giving the enemy team loads of extra time to regroup and contest.

If you're killing the enemy team then they won't be alive to contest the actual push to the goal.

Your goal is killing the enemy team. If the enemy team is dead, they cannot contest the push. You should never, ever have your team just sitting around AFK on the point unless all of the enemies are dead or otherwise unable to be reached. 3 players running in to contest the checkpoint against a full team are just suiciding and adding to their respawn timers. This is a good thing. It means they will not be able to resist the push to the goal as well.

Unless you're the team's designated "okay go AFK on the point" guy, you should never be standing around idle. You should be harassing and killing the remaining enemy players.

[Iyrnwaen]

If you're killing the enemy team then they won't be alive to contest the actual push to the goal.

Your goal is killing the enemy team. If the enemy team is dead, they cannot contest the push. You should never, ever have your team just sitting around AFK on the point unless all of the enemies are dead or otherwise unable to be reached. 3 players running in to contest the checkpoint against a full team are just suiciding and adding to their respawn timers. This is a good thing. It means they will not be able to resist the push to the goal as well.

Unless you're the team's designated "okay go AFK on the point" guy, you should never be standing around idle. You should be harassing and killing the remaining enemy players.

You're dead wrong here, and the prevalence of this attitude loses matches.
Your goal is not to kill the enemy team. Your goal is to push the payload farther than the enemy team.
Taking the checkpoint makes it substantially more difficult for your opponent to prevent an immediate loss in OT.
If you fail to take the checkpoint, you're inviting an OT comeback for your opponents.

5 stacking the checkpoint allows your team to capture it before the enemy team has time to respond.
Leaving one person to slow cap the point gives the enemy team time to contest. You're needlessly creating a risk of failure.
The difference in time to cap between 1 player and 5 players is enormous.

When you choose not to fast cap the point, you're gambling on your split team successfully preventing your opponents from regrouping.
If you fail to do that, your best case scenario is that your team successfully falls back, regroups, and defends the cap.
Your worst case scenario is that respawns pick off members of your team who chase too deep, and the enemy team successfully contests the cap.
Both of those scenarios are worse than simply quick capping the point in the first place and eliminating any risk.