At the beginner stage mixers generally get trashed in favour of an all-in-one interfaces for a number of reasons.
There are plenty of times when a mixer is idea*l, like podcasting/live interviewing/complex routing, patching hardware effects etc, but often it's just unnecessary extra features in exchange for limitations.
If you're talking about an analog output traditional mixer then it's getting plugged into a computer soundcard (usually) which isn't the best way to go for quality.
It also limits you to two simultaneous discrete channels, regardless of how many inputs the mixer has.
If you go with a USB mixer that's maybe a step up (taking the pc sound card out of the loop) but you're generally limited to those two channels again in your DAW, with the budget models.
You can get multichannel usb/firewire mixers, or pair up a mixer with direct outs per channel with a set of converters,
but once you're spending that sort of money you could be buying a great 8 channel interface instead (or two?!).
As I say, plenty of times* the functionality of a mixer is exactly what's needed but at the entry level home recording it's usually not.
* If the extent of your plan is to record solo vocal and a guitar, as separate takes, against a backing track, a little 2 channel USB mixer would be just fine.
A 2 channel USB audio interface would be equally fine.