I guess thought but not said was "why even bother checking the size, it is what it is" — you aren't going to start discarding projects just because the database is over a completely arbitrary size, are you? :-)
You really can skip the whole compaction bit, however, if you just sync regularly and sync before making changes after switching devices (this makes the graph likely to compact sooner, though with only 2 devices it may not matter as much as it does with my 4 to 6). The database isn't going to stay at its minimal size for long if you are using the program, so does it really matter that you know it is completely compacted on the 1st of the month?
Perhaps my tune would be a little different if I frequently had to sync over a 3G or EDGE connection, but even hauling over 10x the freight, I don't find this procedure to be a worthwhile use of my time, as I don't get any appreciable savings. I guess you must feel that you do — do you have any numbers?
How many projects and actions? Rob's OFQuickStats script gives a detailed breakdown:
http://forums.omnigroup.com/showthread.php?t=18405