Hard drives mainly only affect speed when the computer is writing to them, or retrieving from them. If you are using the drive to play some high end game or watching a movie on one, then I would say yes. Otherwise, probably not.
Any that are USB.
They're a little inconvenient to carry around, but they work fine.
One can find more information about external hard drives for laptops from Amazon. The best way to find more information is from the brand of laptop website.
Mac laptops may likely have solid state drives (not hard drives). Those drives are 2.5" form factor and can be replaced by hard drives.
Laptops use 2.5 inch hard drives, while desktops use 3.5 inch hard drives.
There are many portable external hard drives which would fit into most standard size pockets.
The WD Elements has several highly rated external hard drives to choose from, another highly rated brand is the My Passport line of external hard drives.
Laptops have two types of memory, the hard drive (used to store your video, music, and photo files) and RAM (which affects how quickly your computer runs when multiple applications are running). The trend is for newer laptops to have larger hard drives. If you need extra space, portable hard drives are available for external storage.
Western Digital and SeaGate are the top manufacturers of hard drives, internal and external.
Simpletech produce portable external hard drives. These range from small USB sticks, to larger external hard drives. Simpletech also produces mini versions of the portable hard drives
Acer is known for their laptops, but they also produce other computer products. Some of Acer's products include laptop bags, tablet computers, USB drives, external hard drives, desktop computers, and printers.
Hitachi, Seagate, Maxtor