Note, however, that FRAPS doesn't compress audio. You can cut down your files significantly if you re-encode them afterwards with MP3 audio compression. It will save a CHUNK of HD space. Trust me on that!
No. Just keep them regular size until you do whatever video project you plan to do. The audio only accounts for around 1% of the total file size.
Properties of a Fraps file of mine picked at random:
General
Complete name : D:\Fraps\Yak9TestLRearChase6.avi
Format : AVI
Format/Info : Audio Video Interleave
File size : 3.95 GiB
Duration : 2mn 17s
Overall bit rate : 247 Mbps
Video
ID : 0
Format : Fraps
Codec ID : FPS1
Duration : 2mn 17s
Bit rate : 246 Mbps
Width : 1 680 pixels
Height : 1 050 pixels
Display aspect ratio : 1.600
Frame rate : 30.000 fps
Bits/(Pixel*Frame) : 4.643
Stream size : 3.93 GiB (99%)
Audio
ID : 1
Format : PCM
Format settings, Endianness : Little
Format settings, Sign : Signed
Codec ID : 1
Duration : 2mn 17s
Bit rate mode : Constant
Bit rate : 1 411.2 Kbps
Channel(s) : 2 channels
Sampling rate : 44.1 KHz
Bit depth : 16 bits
Stream size : 23.1 MiB (1%)
Interleave, duration : 995 ms (29.86 video frames)