commands like hserin hserout block until they complete whereas in arduino c the equivalents serial.print() and serial.read() are both interrupt driven out of the box . of course pause eqv delay() is a blocker .
but the biggest difference is the architecture of coding style in c most have a main loop that executes as fast as possible calling functions on the way to see if they need servicing each function of course uses time from the main loop but only when needed (think of a token ring) . in basic most programmers make the code like a string doing functions sequentially . no one way is any better than the other except that one strategy may suit some tasks more easily . when it comes to interrupts c wins hands down sure its got to dump a heap of stuff into the stack and pop it off again but its much less than dt-ints doing a pbp style irq quite noticeably in fact , although often it doesn't matter
but what I was trying was three simultaneous async serial streams 2 ser outs one software one hardware and one hardware input all at 9600 baud , both hardware streams interrupt driven . if a chr was lost then things went wrong . in c no chr loss, pbp some loss , arduino mega no loss and baud rate jacked up to 115200 for the debug stream
you have to appreciate commands like serial.available() give you the number of byte in the serial buffer. serial.find("ok") returns true if serial buffer has ok in it . imitating those functions in pbp is not easy (don't forget the buffer is filling in the background as you search and if it overflows all can be lost )

floats are interesting in xc8 /hightec c for pic one float command adds nearly 8k to you pgm so workarounds are very worthwhile . / mikroc pretty much the same sourceboost c has a weird float library that takes multiple steps to achieve and adds up to about the 8k of the others anyway . yet on an arduino you'd hardly notice