"IMHO it is more of a liability than an asset in 8051 embedded systems."

How on earth do you come to that conclusion?

"I reckon 95% or more of the functions have no relevance to embedded systems"

Keil implements all of the standard library that makes sense on an 8051 embedded system which amounts to about two thirds of it. I would estimate that I've used 50-75% of those functions in the time I've been using Keil. I'd be very interested if you would care to name a couple of library functions that Keil implements and explain why you think they are irrelevant to embedded systems.

"and the remainder soon find their way into your own assembly language function library"

I just hate reinventing the wheel.

"YMMV"

I'm afraid I'm not familiar with that one.