Turning on singleplayer automatically grants your Dinos around 90% extra melee.

So if you tame a Rex with let’s say 360% melee, it will be 450% with singleplayer turned on.

Additionally, on officials (for example) every level you put into health gives the dino let’s say 0.95% health, but with singleplayer on its like 1.15% per level, when you spend level ups on health. Melee also gets slightly more per level up than on official stats.

Which in turn, with singleplayer turned on, your tames can reach stats that normally would take you months of breeding to achieve.

For comparison, my current Rexes, zero mutations.

Have 11,000 HP, 368% melee [458% with singleplayer on] on hatch

With 100% imprint and leveled up 45k HP and 1600% melee, that with like 71 out of 88 level ups. (With singleplayer on)

Singleplayer off, those stats become something like 34k hp and 980% melee or something like that. (These aren’t the actual stats, these are just an example for the sake of making a comparison, I am not home right now so I can’t give you the real stats).