I've never been one for a really strict routine, but as DD (18 months) has got older I have come to realise the benefit of having a solid structure to the day which helps with nap times and bedtime.
The problem is that any routine we get into lasts a week/10 days at most then one little thing throws it out of the window, then we have a week or so of erratic napping and overtiredness.
I'm a SAHM and everything seems to go well when I have no commitments/no vistors/no need to be anywhere at a particular time. I can focus on DD and respond to her tired signals. However, something as simple as it being the weekend (when DH is around during the day) can throw everything out of kilter. As an example - last week DD went down for a nap somewhere between 10.30-11.30am every day. This week has been all over the place and yesterday I resorted to taking her for a walk in the pushchair at 3.30pm as she was cranky and overtired but had fought sleep all day.
It gets rather frustrating, not least because it's very difficult to make plans. If I could guarantee a morning nap, then I'd be able to arrange to do things/see people in the afternoon. However, if DD hasn't napped in the morning, then I want to make sure she has one in the afternoon.