Hey, I've been running TuffAnt 18" steel wheels for almost 2 years now (see profile pic). There's been zero negative impact on performance, in fact with better rubber I would argue there is greater performance, however there is an impact on fuel economy of around 10%. My pictured tire is the Hankook RF11 265/65/18's which is a nice all terrain tire, but am now running with a Hercules Terra Trac II, also all terrain. But I digress... there are definite benefits and considerations when weighing up steel vs alloy.
Steel is heavier and look 'purposeful', but as others have mentioned, when dented you can repair yourself off-road with a hammer (not pretty but does the job to get you home), and they can be professionally repaired when you're back in town. They are also more affordable.
Alloy, is lighter, look 'prettier', but they do not dent/warp, they crack. So when they go they go and they cannot be repaired beyond scrapes and gutter rash and are more expensive.
Steel is heavier and look 'purposeful', but as others have mentioned, when dented you can repair yourself off-road with a hammer (not pretty but does the job to get you home), and they can be professionally repaired when you're back in town. They are also more affordable.
Alloy, is lighter, look 'prettier', but they do not dent/warp, they crack. So when they go they go and they cannot be repaired beyond scrapes and gutter rash and are more expensive.