Normally, in TTT2, only certain launching attacks allow for your point character to be tagged out mid combo. If your secondary character then proceeds to damage the opponent, continuing the combo, then the opponent's red life is destroyed for as long as the combo (without using TA) is valid (e.g. WB!, F!, and W! combos). The opportunities for Tag Launching (launch~5) are usually only present in signature launchers (i.e. Mishima EWGF) or large and/or "Hail Mary" type launchers (referred to by a low class number). This doesn't mean that all launchers are equal either; There's a significant amount of tag launchers that lead to your secondary character following up with only quick air jabs to continue the combo. As such the damage potential is much lower as the jabs occur at the beginning of the combo, where the combo scaling is worth the most.
Tag Assault (TA) is a new system mechanic introduced in TTT2 to allow any character (both point and secondary) to be usable in play. Rather than building a team around a certain tag launcher to follow up combo, TA allows the point character to do their normal (or improved) combo, standard bind attack, and then temporarily tag in your secondary character to extend your combo. Once the secondary character completes their string, the point character can proceed to finish the combo with additional hits or set up a possible oki situation. It's a powerful tool as some of the rules seem to change while executing a TA, sometimes opponents will fly high into the air, other times you can sneak in additional hits that normally would not work. Learning what TA moves your character can perform is very important for extending your combo damage/carry potential.
Here's a few basic ideas for figuring out your character's ideal Tag Assault moves
1) Two/Three hit strings, preferably ending with a high attack (as high spike moves usually don't exist, reference to #5)
2) Single strike attacks that are can launch, but not necessarily a launcher, or can be used as filler post launcher
3) Strings with large hit boxes, the smaller the hit box the harder it will be to use
4) Carry strings that end in stances as stances transitions will allow your TA to continue until finished (i.e. Lee b+2~mist)
5) Forced KND (a.k.a spike attack) moves will most likely end your combo immediately but CAN set up wake up oki or reset options.
Tag Assault Classifications:
There is no official terminology, so I've created my own when classifying Tag Assault options. There's two major categories that TA can fall into, namely "Loft" and "Distance". Loft refers to attacks that relaunch the opponent into the air to extend combo length while distance refers to pushing the opponent away. It's important to notice that these satisfy two very different requirements. Loft is useful if your point character has adequate wall carry but is limited on the amount of hits (or overall damage) of their combo. Distance is useful when your point character has above-average damage potential but is lacking respectable wall carry.
That's not to say that they are mutually exclusive though, it's very possible to have a TA that has both loft (to sneak in additional hits) as well as distance (to carry them to the wall). The goal is to find the right balance between loft and distance to cover the deficiencies of your point character, as mentioned in the prior paragraph. If you have two options that are very similar in properties, it would (obviously) be in your best intention to pick a TA with the highest damage or leads to the highest damage potential. Below is a quick chart I made of a few of Dragunov's options and a more select few of the options from the rest of the cast.