It would not give you as good a result. The initial alignment is from the airport ARP, and is downloaded when you enter the airport four-letter ICAO identifier. That gets the alignment process going, even though you may be parked in a bay a couple of miles from the reference point. This is insignificant for the purposes of getting the right latitude for alignment.
If you select NAV right away, as soon as the minimum time necessary for alignment has finished (including the fine tuning), the system will automatically go into NAV mode. If you remain in ALIGN, it will carry on aligning until you select NAV. This may give you extra time aligning, which will give you a more accurate alignment.
Selecting PPOS, or operating the TO/GA lever on take-off, updates the present position in the FMC. It does not alter the raw IRS position, which stays a couple of miles out for the whole trip. However, it is not used in its raw form. Navigation is carried out using the FMC position, which is the final updated position before take-off, carried forward by IRS velocities Kalman-filtered against DME/DME or GPS.