From everything that I've been told (so draw from that what you will), applying later is not as detrimental in psych., as it is in some of the more competitive fields. That having been said, however, it could possibly make scheduling interviews much more chaotic. For instance, suppose that you get two/three interviews in a particular geographic region, ideally you would want to schedule the interviews in blocks to save on money. Applying late, you have limited yourself to dates that are still open; therefore, you may have to geographically double-track on the interview trail which will mean more money.
One last thing, while psych. is less competitive, most psych. programs do have a set number of interview spots; therefore, in a banner year, those spots could fill early. Thus, all things considered, it would behoove applicants to submit their ERAS as soon as is possible--you should still be fine at this point, remember SDNers tend to be a tad overzealous!
