I saved points for weeks and eventually saw my team drop points. Infact, I almost threw away the League.
I can't exactly say it's because I didn't assign them but as soon as I did, my team started winning again.
I don't think it matters what you do really. Personally, I assign mine as soon as I get them.
i do that too .. money saved not worth it .. and skills will slow down anyway once you get X amount of skills a season going one star higher