Dry yeasts and liquid yeasts both have their advantages.
Dry yeast is readily pitchable into wort. Some people suggest re-hydrating it, but I always just dump it in and have <4hour lag times.
Liquid yeast however has a much wider array of styles. There are many liquid yeast styles that don't even exist in the dry yeast market.
That is really the only disadvantage of dry yeast. It used to be thought that there was no way to make dry yeast 100% pure. Meaning that for every 100 million yeast cells, there was a handful of rogue organisms that could potentially ruin a batch of beer. I don't think, if this ever was a problem, that it is a problem now.
My preference is to keep both on hand. I brew mostly English and American style Ales. So I keep about 10 packets of dry yeast on hand. I also buy my grain and hops in bulk, so with dry yeast, if I want to brew on a whim, I can. However, I also brew a number of different ales like Hefeweisen, Kolsch, Altbier, Dubbel etc...these beers require specialized yeast that are only found in the liquid arena. Granted, if I want to brew one of these styles, I have to plan ahead a few days to get a good starter going, but if it were not for these liquid yeasts, I would not be able to brew a proper beer of these styles.
Long story short, if you want to use dry yeast for English and American ales, go right ahead. It is not going to effect anything except the smaller price tag. However, if you plan on brewing more "specialized" beers, you are going to have to use liquid yeast.