For a short trip like the ones BA offers hand baggage fares on, I don't think the drawbacks are that significant (and other posters have captured them), and I'd be inclined to save the £60. If there's an infant on the booking seat selection is free.

For long trips my experience is that it can be quite a hassle including calling BA multiple times to get seats allocated together at bassinet locations etc (compounded if there's multiple airlines on the booking, all of whom require a separate phone call to sort out said seating issues). It should be simple but just doesn't seem to turn out that way!