Basically one to wear with a suit jacket, and a smaller size for times without the suit jacket (i.e. just dress shirt, sweater, etc.) The position I'm looking to accept requires dress shirt and tie 80% of the time, and 20% suit & tie, which is why I'm looking to purchase a the same exact topcoat in 2 different sizes. If I just purchase the smaller size (for dress shirt, no suit) - as for what to do when I actually have to wear my suit, I have not a clue, except maybe hold it in my forearm and then change into it in the office; which may become a hassle down the line if you throw in rain, snow, crowded subway, and travel to client office and home office during the day (intra-city). So I'm possibly thinking of purchasing the same topcoat in two sizes, am i crazy? PS, how hard would it be to tailor a topcoat, primarily take in on the sides and possibly shorten? Thanks.