While effects are an option for any electric instrument, they're borderline standard equipment for the guitar. Desktop and rack guitar effects are flexible additions to your setup that allow you to create complex tonal profiles with a single piece of hardware. Unlike pedals, which are usually dedicated to a particular effect, these desktop and rack-mounted effects processors each offer a selection of sound tweaks to choose from.
Some effects units allow you to emulate the unique characteristics of individual amps and speaker stacks, recreating the sounds of a legendary vintage unit without the hassle of having to hunt one down and restore it. Others make it possible to mix in pre-recorded samples for rhythm and bass accompaniment or playback with a smartphone or portable media player, perfect for solo gigs or busking. If you're into the digital side of things, check out an effects unit with USB connection to download updated profiles or stream digital audio to your laptop's recording software.
There are multiple shapes and sizes of desktop and rack guitar effects to support any application, from spur-of-the-moment jam sessions to permanent studio installations. You can go with a small and light unit that fits in the palm of your hand for ultimate portability, or upgrade to a bigger desktop effects processor to exchange some of that mobility for an expanded list of features. The largest units are rack-mounted, perfect for your home recording studio or a road case rack when you're on tour. Big rack-mounted units are the least portable, but they make up for that by having the most features, with tons of presets and effects as well as more physical connectors and jacks to plug in all of your other audio equipment.
Narrowing down your options in desktop and rack guitar effects is all about finding the balance between features, connectivity and portability that fits your needs. Take a look at the effects that come pre-loaded, decide how you'll be using the effects unit, and make your decision from there.