Cuba sent hundreds of thousands of soldiers into Africa. They fought, most famously, in the Angolan civil war but also against the Eritrean rebels and Somalia for Ethiopia, against South Africa for Angola and Mozambique, against Morocco for Algeria, etc, etc.
There were Cuban military advisors operating in 24 African countries during the 80s, just to pick an example at random, Bob Denard attempted to overthrow Benin's government because Cuba attempted to rent a military base in Benin from them. Generally speaking communism in Africa during the cold war was supported by soviet money and arms but by Cuban manpower.
If Castro doesn't become leader of Cuba and there is no flow of Cuban soldiers into Africa, then what effect does that have on the socialist movements in Africa? Does Ethiopia collapse in the 1970s? Does apartheid hang on a little longer? Does UNITA take over in Angola?