The save game folder size doesn't matter (although the list of save games might take longer to load if you have hundreds of save games in the folder). The size of a single save game is what matters. I think at ~10mb size (per single save game) the save game can become corrupt and unusable. That happens mainly due to bugs in scripts added by mods (although the causes for save game bloating are well known so you will have trouble finding mods that cause save game bloating nowadays).
My save game folder is 439mb large and the average save game size for my level 25 character is 4mb.
Wow thanks again Phitt good advice

Ok, well yeah I run a few mods (about 30) and have quite a few game saves (about 10 or more I think). I just checked my most recent save and it was 4.5 mbs, so that's good right?