blue points

[Md3blue]

what is the blue points used for?

[Fulysic]

Scrap points used for repairs I. Certain areas

[Maniachanical]

Can be used to increase the values of parts. On performance parts, it also increases its HP boost.

[Szczurexon]

Ty for answer

[astrofelix59]

To do a whole car at 3 star will use ~23,000 points, the scrap from +20 builds (best case hit rate), to add ~3% $ value.
i.e. average scrap parts per build about 120, you'll get 120-450 points (pending hit rate) or or about $1,500 to just sell the junk.
So you will make more money selling the scrap, unless you are doing it to a car worth more than 2 million to begin with.

For performance parts, at 3 star it will add 10-15% boost and cost about 7,000 points. Good to max out cars under 500HP (base HP) but generally doesn't help for the Race Track, where you need a balance of power and control (less is more kind of deal), you should be able to get enough juice with performance parts alone.
For the Drag strip, yeah max the ♥♥♥♥ out of them.

If you get the blues from chests only (payout scaled to Level), it's viable but still a waste of time. If you use QoL mod and cheat them, then have at it.

Note: I give a few favourite race cars the full treatment, because they are special and I have the points. (numbers above are low balled)