Even at 320Kbps, standard compression formats remove portions of data from the original source material to attain very small file sizes.
WMA Lossless does not remove any data, so audio quality is not sacrificed in any way. You pay for this with larger file sizes (but file sizes one-half to one-third the size of the original, with zero quality loss). If you don't mind a difference (no matter how slight) in audio quality, and your aim is to store/use music the way you currently use mp3s, you would use the regular WMA 9 CBR or VBR codecs. In this case, you will get audio quality that is generally better than mp3 or mp4, and has smaller file sizes.
Think of WMA Lossless as you would .zip-style file compression. If you were to compress a document using zip, you get the exact same document back when you unzip it. This is because zip uses lossless compression.
If zip used lossy compression, you would not be able to get back the document that you put in. The document you get back would be corrupted because data was taken out during the compression process that you can't get back.
This is how regular, lossy compression formats (WMA CBR/VBR, MP3, MP4, Ogg, etc.) work. Algorithms are used by the encoder to remove portions of the audio data that most people aren't likely to notice or care about substantially. Depending on how good your ears are, you may be able to detect the results of the missing audio data more or less depending on the encoding settings.
Other than being able to hear the results of loss of data, you also will continue to reduce the quality of your encoded audio if you try to convert it to other lossy formats (such as taking a WMA, converting to MP3, then MP4, then Ogg, etc.). If you want the highest quality whenever a new format comes out, you must go back to the original source material, or if you use lossless compression like WMA Lossless, the quality of the encoded material is always equal to the quality of the original source.
This is a crude example, but it is basically like this:
If your original source material were represented as a decimal value like 1.23456
WMA Lossless preserves this exact same value 1.23456
Normal, lossy codecs (WMA CBR/VBR, MP3, MP4, etc.) would round this value because the major aim is small file size with limited quality loss. So you may end up with 1.2
This is not the same data you started with, and each time you convert it to another lossy format, you lose even more data. So you next encoding of the song may give you 1, then .8, then you will eventually get to the point where the song is unrecognizable because each lossy conversion takes away more data.