i finished making my ST 1x1 SA and AMR/AMC shaddow striker SA
you only do that if :
1-you can afford 50 Green packs
2-they are fast trainer (to know if one is fast trainer, if you hit 10% stretching training in normal, he should get 18-20 skills points in average if he is 5*, more if he is 4* and more if 3*..etc)
3- he is 18 yo or max 19 yo.. just to make sure is a long term investment that make it worth it
4- the earlier you apply, the better, ex: 3* fast trainer, will make you consume less than 50 green packs, 4* will make you consume around 50, 5* will make you consume between 50-60 green packs
5- in my last case for last 2 players, one player I trained him till he was close to next star and stopped 15 skills points away, and started to apply for SA, bcz once i hit new star levels, he will develop slower ..bcz i needed him .. but the other one, i applied SA first as was not that much needed
6- is important if you are close to next level, to apply skills points to SA once you get them, let us say you are 15 skills points far from new star level, if you collected 15skills points and never applied it to SA, game will considered you reached new star level, so what i did is to apply them straightway with no delays (thanks for July fourth for that tips)