If I'm going to reload, when time and conditions permit, then I don't want to drop a partially loaded magazine onto asphalt/concrete where it might break and become useless.
If there's an imminent threat, then it doesn't make sense to reload a gun that doesn't need reloading in the first place. But if you, for some reason, do decide to reload while an imminent threat exists but when you don't actually have to, your priority should still be getting your gun running again as fast as possible. Dropping a magazine should be so low on your list of priorities that it shouldn't even register.
If there's no threat then take your time and reload any way you want. It doesn't matter how you do it nor how long it takes since time isn't an issue.
It's an option I employ when I make a decision that I want to quickly restore my weapon to full battle-readiness status.
If you really need to do that (i.e. imminent threat exists), then you also need to do it as fast as possible. If you don't really NEED your weapon to be at full battle-readiness status (i.e. no imminent threat exists) then reload however you want and take as long as you want. If there's no imminent threat it doesn't matter how you reload.
The ONLY difference in time between a Tactical Reload and a Combat Reload is the fraction of a second it takes to manually remove the partially depleted magazine before inserting and seating the fresh magazine.
That's not true unless you drop the partially depleted magazine after manually removing it--which would be ludicrous.
You obviously also have to put the magazine away or it wouldn't make any sense at all to remove it manually in the first place. And until you've done that and returned your support hand back to its grip you will be unnecessarily handicapped by having to use your weapon with only one hand, or at the least by having to try to grip the gun and hold onto the magazine at the same time.
From fully ready back to to fully ready (apples to apples comparison) comparing a speed relaod to a tac-reload is more than a "fraction of a second" of difference.
How about if I find myself in a mall or movie theater mass shooting situation and I've exchanged shots and the bad guy(s) have moved on to easier targets. I may desire to quickly top off my pistol (and retain my partially depleted magazine) before I sprint to an exit in case I encounter a bad guy(s) enroute and have to continue the fight. (In this case I don't want to jettison my partially depleted magazine onto a hard floor where it could burst apart.) I don't have to think about what I'm doing when I perform a Tactical Reload - I just do it because it's as natural to me as as loading my pistol.
In this scenario there is no imminent threat because "the bad guy has moved on". So reload however you want--with no imminent threat it doesn't matter what you do.
This is very simple from a logical standpoint.
If there IS an imminent threat and you have a running gun, it makes no sense to stop and reload if you don't have to. If you DO have to reload then reload as fast as you can.
If there is NO imminent threat then any technique that's reasonable and that meets whatever personal requirements you can dream up is just fine.
It's only when there IS a threat and there is NO threat simultaneously that it makes sense to keep the partially loaded mag (because of the imminent threat) and take more time than necessary doing the reload (because there is no imminent threat). That's what I mean when I say it takes tortured logic to justify a tac-reload.