I;ve been doing this for quite a while with DS (2.3) as he just won't nap at home - unless I put the tv on after lunch which I'm not that keen to do as it's already been on too much in the morning. I do it sometimes though and he invariably falls asleep on the sofa.
I know he still needs this nap as he still does it in nursery and he always falls asleep when we go out in the car after lunch.
Obviously I would prefer it if he did nap in te house because I could get chores done but as it is, I use this time to rest and read my book and sometimes have a little nap myself . I'm six months pregnant so indulge myself a little while I just have one DC!