If the mother herself is handled a lot and used to humans, she usually won't mind a human coming to handle her chicks. I made sure to spend time every day handling each of the chicks my broody hatched. The lady I sold them too said she'd never had such friendly, active, inquisitive babies...
Eggs can get accidentally squished if the hen is a large breed (like an 8 lb brahma) and has too many under her without enough bedding to cushion things. Since some of my urban flock have proven to be stubborn broodies (namely my bantam wyandotte and cochin/d'uccle mix), I also enjoy watching...
alot of those cons can be avoided with good flock management..
Egg abandonment -- don't immediately give a broody eggs, especially if she's a first timer or has a history of being flakey about it. My frizzled cochin would be "broody" for 2 days and then give up for a week, then go again for 2...
Honestly.. I didn't keep track after I let my broody hen hatch hers last time.. she decided to molt right afterwards too, so that took awhile for her to grow all her feathers back and lay again.
She'll start refusing to leave her chosen nesting spot for long periods. If you approach she'll give a warning growl or trill to make you go away (channeling her inner t-rex). She may also 'flatten' herself over the nest box until she resembles a feathery pancake that growls. If you actually...