As far as the functional purpose of the Kaempfer, the standard explanation is pretty much just what I already quoted from the MG kit manual. The highlights once again:
This was a specialized machine with the ability to singlehandedly engage in anti-mobile suit combat and penetrate enemy defensive lines. (The term "kampf" includes the meaning of melee combat.) It could make hit-and-run attacks using the high-output vernier thrusters installed throughout its body, overcoming the enemy's bases and main forces. [...] it could also be said that virtually no consideration was given to "returning" after the assault.
The Kaempfer is normally described as an "assault mobile suit," a term used to describe a variety of other machines. But it's worth noting that there actually two
terms used in Gundam, both of which are translated as "assault" but which have slightly different shades of meaning. Specifically:強襲
) - more like a surprise attack or raid.突撃
) - more like a frontal charge against the enemy lines.
The term 強襲 is the one that's always used to describe the Kaempfer and the Gerbera Tetra. It also features in the classification of the White Base (強襲揚陸艦, or "assault landing ship") and the name of the RTX-440 Assault Guntank (陸戦強襲型ガンタンク). According to the MG kit manuals, the Gundam GP02A was originally planned as an "assault" or "raiding" mobile suit in this same category.
One thing that most of these "raiding" machines have in common is good close combat weaponry. They all have vulcans for close defense, and the Gerbera Tetra also has forearm machine guns of the same type that defeated its predecessor. The Kaempfer, GP02A, and Gerbera Tetra even use similar hip-mounted beam saber racks, and the attack methods of the Kaempfer and GP02A are fairly similar - deal a devastating blow to the enemy forces with long-range weapons, then charge in and finish off the survivors in melee combat. Some writeups on the Gerbera Tetra, such as the one on the official Gundam 0083 web site, suggest that it was meant to work the same way:
Because it inherited the concept of being "the strongest in anti-mobile suit combat," it had superb melee and hand-to-hand combat capabilities, and it was also equipped with a sturm booster to make it easier to transition into melee combat.
The aforementioned "Gundam The Movies" writeup makes much of the Kaempfer's emphasis on close combat, and claims that this the real reason for its limited use of beam weapons - their damage level is harder to control in close combat, and they're more likely to provoke generator explosions that would destroy the Kaempfer as well.
What about the second kind of "assault"? The term 突撃 seems to be used more for a mass frontal assault on enemy lines. This is used to describe the Public and Jicco assault boats from the One Year War, MS-X machines such as the Gassha and Pezun Dowadge, the Federation's GM Striker and GM Cannon Space Assault Type, and of course the Dra-C. The description of the Pezun Dowadge from the Zeonography box, however, makes this category sound fairly similar:
It is meant to be an "assault type" which, in addition to the functions of the Dom, can use its heavy armor for anti-MS melee combat, and even takes hand-to-hand combat into account.
Finally, the standard description of the Zssa encompasses both terms. The profile from the Gundam Collection mini-figure series elaborates on this at some length:
A support mobile suit developed for joint operations with the AMX-101 Galluss-J. Its main roles are raiding attacks and rear support, and it could be considered a successor to the concept of the MS-13 Gassha from the MS-X category developed by the former Principality forces. When equipped with a booster, it can also fly in the atmosphere, and in functional terms it could be called a mobile suit version of the space assault boats of the One Year War era. Naturally, it can also function as a mobile suit, and can even handle close combat with its beam sabers. Compared to the average machine of its time, it would be categorized as a small machine. But when the boosters and missile pods are removed to preserve its maneuverability, it could be described as having rather excellent hand-to-hand combat capabilities.
So this is a pretty similar mission profile to the Public, the Kaempfer, the Gundam GP02A, and the Gerbera Tetra: Approach at high speed, unload a lot of heavy firepower at the main body of the enemy, and then ditch all the dead weight and mop up the survivors in close combat. It's a fairly complicated mission profile compared to normal mobile suit types, and judging from the animation these machines do tend to have a low survival rate, since we've never really seen them return in one piece. On the other hand, they do seem to be pretty effective!