Hi,
Short answer: the effects seen are designed to replicate the RW effect of replacing some of the medium tanks in the normal TO&E of your applicable divisions. This is sort of a mixed bag as some nations did this pretty routinely while others did not.
Light Tanks: Lower cost (build, supply, oil), easy to maintain (+MOR) and better mobility (terrain bonuses). OTOH lower combat capability (-ORG). Most nations discontinued production of these type vehicles rather quickly as they just we're effective in combat. Good for nations with higher ORG than MOR, such as the SOV, which used these much longer than most.
Heavy Tanks: Strong in combat (+ORG). OTOH, higher cost (build, supply, oil), hard to maintain (-MOR) and poor mobility (terrain penalties). Good for nations that want maximum ORG and that will build the attachments as well. Basically GER/SOV in late game.
mm