Sometimes I get emails where ladies send me pictures of their bicycle and ask whether I think "it would look better" with dress guards and/or a chaincase. Ladies... You do realise that these things are not there for the looks, right? Although a set of dress guards and a chaincase do lend a certain charm to a bicycle, aesthetics are not their primary purpose. So let me explain why I put them on my bikes, and then you can decide for yourself whether you need them or not.
The purpose of dress guards is to stop fluttery, loose clothing from flying into the spokes of your rear wheel and either getting ruined or causing an accident. The main determinant of whether you need dressguards is whether you wear the sort of clothing that requires their protection - for instance: flared skirts, dresses, long coats, or flowing tunics. Once you have had something get stuck in your rear spokes or have seen it happen to someone else, you know that the possibility is real and that it can even cause injury. Personally, I will not ride a bicycle without dress guards if an article of clothing I am wearing is long enough to reach the rear spokes. And since much of my everyday clothing is in that category, it is a good idea for me to install dress guards on any bike I plan to use for transportation.
I have also been asked what kind of dressguards are better: netted or solid. There are probably differing opinions on this, but in my experience it does not matter. My vintage Raleigh (above) is fitted with very minimal dressguards that are basically just stretchy cords fanning out from the rear dropouts. For me, this has been sufficient; the cords - closely spaced - provide a perfectly functional barrier. The obvious advantage to dress guards that are woven, is that they are lighter (and usually more attractive) than plastic ones. The disadvantage is that they can be more expensive and more difficult to clean.
Moving on to chaincases, their purpose is two-fold: (1) to prevent the bottoms of your trousers from being caught in the chain, and (2) to keep the chain clean from street grime, especially in bad weather. Since I seldom wear long trousers, the first function is not that important to me. So while I do appreciate that the chaincase keeps my chain nice and clean, this accessory is not as crucial for me as dress guards, because it is a maintenance feature rather than a safety feature. I can still ride a bike without a chaincase for transportation.
Furthermore, while I have found dress guards to be effective in preventing clothing from getting stuck in the spokes, I have not found chaincases to be entirely effective on those rare occasions when I do wear trousers. A couple of times, the bottoms of my trousers have actually gotten stuck on the chaincase itself, which has only increased my bias for skirts once I started cycling. Don't get me wrong, I still love a nice, elegant chaincase. But I admit that this feature does not hold as much functional purpose for me as do dress guards.
Dress guards and chaincases are not affectations, but necessary accessories for transportation in everyday clothing. As the popularity of "city bikes" rises, I hope that more American bicycle shops will realise this, and start carrying these useful items.